Recent Postings from Galactic

The SAMI Galaxy Survey: Towards a unified dynamical scaling relation for galaxies of all types

We take advantage of the first data from the Sydney-AAO Multi-object Integral field (SAMI) Galaxy Survey to investigate the relation between the kinematics of gas and stars, and stellar mass in a comprehensive sample of nearby galaxies. We find that all 235 objects in our sample, regardless of their morphology, lie on a tight relation linking stellar mass ($M_{*}$) to internal velocity quantified by the $S_{0.5}$ parameter, which combines the contribution of both dispersion ($\sigma$) and rotational velocity ($V_{rot}$) to the dynamical support of a galaxy ($S_{0.5}=\sqrt{0.5V_{rot}^{2}+\sigma^{2}}$). Our results are independent of the baryonic component from which $\sigma$ and $V_{rot}$ are estimated, as the $S_{0.5}$ of stars and gas agree remarkably well. This represents a significant improvement compared to the canonical $M_{*}$ vs. $V_{rot}$ and $M_{*}$ vs. $\sigma$ relations. Not only is no sample pruning necessary, but also stellar and gas kinematics can be used simultaneously, as the effect of asymmetric drift is taken into account once $V_{rot}$ and $\sigma$ are combined. Our findings illustrate how the combination of dispersion and rotational velocities for both gas and stars can provide us with a single dynamical scaling relation valid for galaxies of all morphologies across at least the stellar mass range 8.5$<log(M_{*}/M_{\odot})<$11. Such relation appears to be more general and at least as tight as any other dynamical scaling relation, representing a unique tool for investigating the link between galaxy kinematics and baryonic content, and a less biased comparison with theoretical models.

Radio-Quiet Quasars in the VIDEO Survey: Evidence for AGN-powered radio emission at S_1.4GHz < 1 mJy

Understanding the interplay between black-hole accretion and star formation, and how to disentangle the two, is crucial to our understanding of galaxy formation and evolution. To investigate, we use a combination of optical and near-infrared photometry to select a sample of 74 quasars from the VISTA Deep Extragalactic Observations (VIDEO) Survey, over 1 deg^2. The depth of VIDEO allows us to study very low accretion rates and/or lower-mass black holes, and 26 per cent of the candidate quasar sample has been spectroscopically confirmed. We use a radio-stacking technique to sample below the nominal flux-density threshold using data from the Very Large Array at 1.4 GHz and find, in agreement with other work, that a power-law fit to the quasar-related radio source counts is inadequate at low flux density. By comparing with a control sample of galaxies (where we match in terms of stellar mass), and by estimating the star formation rate, we suggest that this radio emission is predominantly caused by accretion activity rather than star-formation activity.

Quantifying the Heating Sources for Mid-infrared Dust Emissions in Galaxies: The Case of M 81

With the newly available SPIRE images at 250 and 500 micron from Herschel Space Observatory, we study quantitative correlations over a sub-kpc scale among three distinct emission components in the interstellar medium of the nearby spiral galaxy M 81 (NGC 3031): (a) $I_{8}$ or $I_{24}$, the surface brightness of the mid-infrared emission observed in the Spitzer IRAC 8 or MIPS 24 micron band, with $I_8$ and $I_{24}$ being dominated by the emissions from Polycyclic Aromatic Hydrocarbons (PAHs) and very small grains (VSGs) of dust, respectively; (b) $I_{500}$, that of the cold dust continuum emission in the Herschel SPIRE 500 micron band, dominated by the emission from large dust grains heated by evolved stars, and (c) $I_{{\rm H}\alpha}$, a nominal surface brightness of the H$\alpha$ line emission, from gas ionized by newly formed massive stars. The results from our correlation study, free from any assumption on or modeling of dust emissivity law or dust temperatures, present solid evidence for significant heating of PAHs and VSGs by evolved stars. In the case of M 81, about 67% (48%) of the 8 micron (24 micron) emission derives its heating from evolved stars, with the remainder attributed to radiation heating associated with ionizing stars.

RAyMOND: An N-body and hydrodynamics code for MOND

The LCDM concordance cosmological model is supported by a wealth of observational evidence, particularly on large scales. At galactic scales, however, the model is poorly constrained and recent observations suggest a more complex behaviour in the dark sector than may be accommodated by a single cold dark matter component. Furthermore, a modification of the gravitational force in the very weak field regime may account for at least some of the phenomenology of dark matter. A well-known example of such an approach is MOdified Newtonian Dynamics (MOND). While this idea has proven remarkably successful in the context of stellar dynamics in individual galaxies, the effects of such a modification of gravity on galaxy interactions and environmental processes deserves further study. To explore this arena we modify the parallel adaptive mesh refinement code RAMSES to use two formulations of MOND. We implement both the fully non-linear aquadratic Lagrangian (AQUAL) formulation as well as the simpler quasi-linear formulation (QUMOND). The relevant modifications necessary for the Poisson solver in RAMSES are discussed in detail. Using idealised tests, in both serial and parallel runs, we demonstrate the effectiveness of the code.

Extended Main Sequence Turnoffs in Intermediate-Age Star Clusters: A Correlation Between Turnoff Width and Early Escape Velocity [Replacement]

We present color-magnitude diagram analysis of deep Hubble Space Telescope imaging of a mass-limited sample of 18 intermediate-age (1 – 2 Gyr old) star clusters in the Magellanic Clouds, including 8 clusters for which new data was obtained. We find that ${\it all}$ star clusters in our sample feature extended main sequence turnoff (eMSTO) regions that are wider than can be accounted for by a simple stellar population (including unresolved binary stars). FWHM widths of the MSTOs indicate age spreads of 200-550 Myr. We evaluate dynamical evolution of clusters with and without initial mass segregation. Our main results are: (1) the fraction of red clump (RC) stars in secondary RCs in eMSTO clusters scales with the fraction of MSTO stars having pseudo-ages $\leq 1.35$ Gyr; (2) the width of the pseudo-age distributions of eMSTO clusters is correlated with their central escape velocity $v_{\rm esc}$, both currently and at an age of 10 Myr. We find that these two results are unlikely to be reproduced by the effects of interactive binary stars or a range of stellar rotation velocities. We therefore argue that the eMSTO phenomenon is mainly caused by extended star formation within the clusters; (3) we find that $v_{\rm esc} \geq 15$ km/s out to ages of at least 100 Myr for ${\it all}$ clusters featuring eMSTOs, while $v_{\rm esc} \leq 12$ km/s at all ages for two lower-mass clusters in the same age range that do ${\it not}$ show eMSTOs. We argue that eMSTOs only occur for clusters whose early escape velocities are higher than the wind velocities of stars that provide material from which second-generation stars can form. The threshold of 12-15 km/s is consistent with wind velocities of intermediate-mass AGB stars in the literature.

Extended Main Sequence Turnoffs in Intermediate-Age Star Clusters: A Correlation Between Turnoff Width and Early Escape Velocity

We present color-magnitude diagram analysis of deep Hubble Space Telescope imaging of a mass-limited sample of 18 intermediate-age (1 – 2 Gyr old) star clusters in the Magellanic Clouds, including 8 clusters for which new data was obtained. We find that ${\it all}$ star clusters in our sample feature extended main sequence turnoff (eMSTO) regions that are wider than can be accounted for by a simple stellar population (including unresolved binary stars). FWHM widths of the MSTOs indicate age spreads of 200-550 Myr. We evaluate dynamical evolution of clusters with and without initial mass segregation. Our main results are: (1) the fraction of red clump (RC) stars in secondary RCs in eMSTO clusters scales with the fraction of MSTO stars having pseudo-ages $\leq 1.35$ Gyr; (2) the width of the pseudo-age distributions of eMSTO clusters is correlated with their central escape velocity $v_{\rm esc}$, both currently and at an age of 10 Myr. We find that these two results are unlikely to be reproduced by the effects of interactive binary stars or a range of stellar rotation velocities. We therefore argue that the eMSTO phenomenon is mainly caused by extended star formation within the clusters; (3) we find that $v_{\rm esc} \geq 15$ km/s out to ages of at least 100 Myr for ${\it all}$ clusters featuring eMSTOs, while $v_{\rm esc} \leq 12$ km/s at all ages for two lower-mass clusters in the same age range that do ${\it not}$ show eMSTOs. We argue that eMSTOs only occur for clusters whose early escape velocities are higher than the wind velocities of stars that provide material from which second-generation stars can form. The threshold of 12-15 km/s is consistent with wind velocities of intermediate-mass AGB stars in the literature.

The Hector Survey: integral field spectroscopy of 100,000 galaxies

In March 2013, the Sydney–AAO Multi-object Integral field spectrograph (SAMI) began a major survey of 3400 galaxies at the AAT, the largest of its kind to date. At the time of writing, over a third of the targets have been observed and the scientific impact has been immediate. The Manga galaxy survey has now started at the SDSS telescope and will target an even larger sample of nearby galaxies. In Australia, the community is now gearing up to deliver a major new facility called Hector that will allow integral field spectroscopy of 100 galaxies observed simultaneously. By the close of the decade, it will be possible to obtain integral field spectroscopy of 100,000 galaxies over 3000 square degrees of sky down to r=17 (median). Many of these objects will have HI imaging from the new ASKAP radio surveys. We discuss the motivation for such a survey and the use of new cosmological simulations that are properly matched to the integral field observations. The Hector survey will open up a new and unique parameter space for galaxy evolution studies.

Impact of radial migration on stellar and gas radial metallicity distribution

Radial migration is defined as the change in guiding centre radius of stars and gas caused by gains or losses of angular momentum that result from gravitational interaction with non-axisymmetric structure. This has been shown to have significant impact on the metallicity distribution in galactic discs, and therefore affects the interpretation of Galactic archeology. We use a simulation of a Milky Way-sized galaxy to examine the effect of radial migration on the star and gas radial metallicity distribution. We find that both the star and gas component show significant radial migration. The stellar radial metallicity gradient remains almost unchanged but the radial metallicity distribution of the stars is broadened to produce a greater dispersion at all radii. However, the metallicity dispersion of the gas remains narrow. We find that the main drivers of the gas metallicity distribution evolution are metal enrichment and mixing: more efficient metal enrichment in the inner region maintains a negative slope in the radial metallicity distribution, and the metal mixing ensures the tight relationship of the gas metallicity with the radius. The metallicity distribution function reproduces the trend in the age-metallicity relation found from observations for stars younger than 1.0 Gyr in the Milky Way.

Flip-flopping binary black holes

We perform a full numerical simulation of binary spinning black holes to display the long term spin dynamics. We start the simulation at an initial proper separation between holes of d~25M and evolve them down to merger for nearly 48 orbits, 3 precession cycles and half of a flip-flop cycle. The simulation lasts for t=20000M and displays a change in the orientation of the spin of the secondary black hole from initially aligned with the orbital angular momentum to a complete anti-alignment after half of a flip-flop cycle. This process continuously flip-flops the spin during the lifetime of the binary. We discuss the consequences of this oscillation mode for accreting binaries, in particular for the spin growth and binary dynamics as well as the observational consequences for galactic and supermassive black holes.

Flip-flopping binary black holes [Cross-Listing]

We perform a full numerical simulation of binary spinning black holes to display the long term spin dynamics. We start the simulation at an initial proper separation between holes of d~25M and evolve them down to merger for nearly 48 orbits, 3 precession cycles and half of a flip-flop cycle. The simulation lasts for t=20000M and displays a change in the orientation of the spin of the secondary black hole from initially aligned with the orbital angular momentum to a complete anti-alignment after half of a flip-flop cycle. This process continuously flip-flops the spin during the lifetime of the binary. We discuss the consequences of this oscillation mode for accreting binaries, in particular for the spin growth and binary dynamics as well as the observational consequences for galactic and supermassive black holes.

Reconstructing the star formation history of the Milky Way disc(s) from chemical abundances

We develop a chemical evolution model in order to study the star formation history of the Milky Way. Our model assumes that the Milky Way is formed from a closed box-like system in the inner regions, while the outer parts of the disc experience some accretion. Unlike the usual procedure, we do not fix the star formation prescription (e.g. Kennicutt law) in order to reproduce the chemical abundance trends. Instead, we fit the abundance trends with age in order to recover the star formation history of the Galaxy. Our method enables one to recover with unprecedented accuracy the star formation history of the Milky Way in the first Gyrs, in both the inner (R<7-8kpc) and outer (R>9-10kpc) discs as sampled in the solar vicinity. We show that, in the inner disc, half of the stellar mass formed during the thick disc phase, in the first 4-5 Gyr. This phase was followed by a significant dip in the star formation activity (at 8-9 Gyr) and a period of roughly constant lower level star formation for the remaining 8 Gyr. The thick disc phase has produced as many metals in 4 Gyr as the thin disc in the remaining 8 Gyr. Our results suggest that a closed box model is able to fit all the available constraints in the inner disc. A closed box system is qualitatively equivalent to a regime where the accretion rate, at high redshift, maintains a high gas fraction in the inner disc. In such conditions, the SFR is mainly governed by the high turbulence of the ISM. By z~1 it is possible that most of the accretion takes place in the outer disc, while the star formation activity in the inner disc is mostly sustained by the gas not consumed during the thick disc phase, and the continuous ejecta from earlier generations of stars. The outer disc follows a star formation history very similar to that of the inner disc, although initiated at z~2, about 2 Gyr before the onset of the thin disc formation in the inner disc.

A HST/COS survey of molecular hydrogen in DLAs & sub-DLAs at z < 1: Molecular fraction and excitation temperature

We present the results of a systematic search for molecular hydrogen (H2) in low redshift (0.05 < z < 0.7) damped and sub-damped Lya absorption systems (DLAs/sub-DLAs) with N(HI) > 10^19.0 cm^{-2}, in the archival Hubble Space Telescope (HST)/Cosmic Origins Spectrograph (COS) spectra. Our core sample is comprised of 27 systems with a median log N(HI) = 19.6. This is a factor of ~ 10 lower than that of the high-z (z > 2) sample of Noterdaeme et al. H2 absorption is detected in 10 cases (3/5 in DLAs and 7/22 in sub-DLAs). On the average, our survey is sensitive down to log N(H2) = 14.4 corresponding to a molecular mass fraction of log f_H2 = -4.9 at the median N(HI). The H2 incidence rate of 50^{+25}_{-12} percent, is a factor of > 2 higher than that of the high-z sample, for systems with N(H2) > 10^14.4 cm^{-2}. The enhanced incidence rate could result from the increase of the cosmic mean metallicities of DLAs and sub-DLAs with cosmic time. In spite of having systematically lower N(HI) values, low-z H2 systems show molecular mass fractions (log f_H2 = -1.93 $\pm$ 0.63) that are comparable to the high-z measurements. The rotational excitation temperatures (T_01 = 133 $\pm$ 55 K), as measured in our low-z sample, are typically consistent with high-z measurements. Simple photoionization models demonstrate that the radiation field prevailing in the low-z H2 systems cannot have an appreciable stellar contribution for densities of 10-100 cm^{-3}. The impact parameters of the nearest possible host-galaxy candidates are typically large (e.g. 10 < $\rho$ (kpc) < 80). We, therefore, conjecture that the low-z H2 bearing gas is not related to star-forming disks but stems from self-shielded, tidally stripped or ejected disk-material in the extended halo.

Growing galaxies via superbubble-driven accretion flows

We use a suite a cooling halo simulations to study a new mechanism for rapid accretion of hot halo gas onto star-forming galaxies. Correlated supernovae events create converging ‘superbubbles’ in the halo gas. Where these collide, the density increases, driving cooling filaments of low metallicity gas that feed the disc. At our current numerical resolution (20 pc) we are only able to resolve the most dramatic events; these could be responsible for the build-up of galaxy discs after the most massive gas-rich mergers have completed (z < 1). As we increase the numerical resolution, we find that the filaments persist for longer, driving continued late-time star formation. This suggests that SNe-driven accretion could act as an efficient mechanism for extracting cold gas from the hot halo, driving late-time star formation in disc galaxies. We show that such filament feeding leads to a peak star formation rate (SFR) of $\sim 3$ M$_{\rm sun}$ yr$^{-1}$, consistent with estimates for the Milky Way. By contrast, direct cooling from the hot halo (‘hot-mode’ accretion, not present in the simulations that show filament feeding) falls short of the SNe-driven SFR by a factor of 3-4, and is sustained over a shorter time period. The filaments we resolve extend to $\sim$ 50 kpc, reaching column densities of $\sim 10^{18}$ cm$^{-2}$. We show that such structures can plausibly explain the broad dispersion in Mg II absorption seen along sight lines to quasars. Our results suggest a dual role for stellar feedback in galaxy formation, suppressing hot-mode accretion while promoting cold-mode accretion along filaments. This ultimately leads to more star formation, suggesting that the positive feedback effect outweighs the negative. Finally, since the filamentary gas has higher angular momentum than that coming from hot-mode accretion, we show that this leads to the formation of substantially larger gas discs.

Expanded haloes, abundance matching and too-big-to-fail in the Local Group

Observed kinematical data of 40 Local Group members are used to derive the dark matter halo mass of such galaxies. Haloes are selected from the theoretically expected Local Group mass function and two different density profiles are assumed, the standard NFW model and a mass dependent profile which accounts for the effects of baryons in modifying the dark matter distribution within galaxies. The resulting relations between stellar and halo mass are compared with expectations from abundance matching. Using the NFW profile, the ensemble of Local Group galaxies is generally fit in relatively low mass haloes, leaving dark many massive haloes of Mhalo>10^10Msun: this reflects the "too big to fail" problem in the Local Group and results in a Mstar-Mhalo relation that differs from abundance matching predictions. Moreover, the star formation efficiency of isolated Local Group galaxies increases with decreasing halo mass when adopting a NFW model. By contrast, using the mass dependent density profile, relatively high stellar mass (Mstar>10^6Msun) dwarf galaxies are assigned to more massive haloes, which have a central cored distribution of dark matter: the "too big to fail" problem is alleviated, the resultant Mstar-Mhalo relation follows abundance matching predictions down to the completeness limit of current surveys, and the star formation efficiency of isolated members decreases with decreasing halo mass, in agreement with theoretical expectations. Several low mass (Mstar<10^6Msun) satellite galaxies are best fit to lower mass haloes than expected from the extrapolation of abundance matching relations, which may result from environmental effects, a scenario favored by the fact that no isolated galaxies fall in this region. Finally, the cusp/core space of Local Group galaxies is presented, providing a framework to understand the non-universality of their density profiles.

Sculpting the Stellar Cusp in the Galactic Center [Cross-Listing]

Observations of the innermost parsec surrounding Sgr A* —the supermassive black hole in the center of our Galaxy— have revealed a diversity of structures whose existence and characteristics apparently defy the fundamental principles of dynamics. In this article, we review the challenges to the dynamics theories that have been brought forth in the past two decades by the observations of the Galactic center (GC). We outline the theoretical framework that has been developed to reconcile the discrepancies between the theoretical predictions and the observational results. In particular, we highlight the role of the recently discovered sub-parsec stellar disk in determining the dynamics and resolving the inconsistencies. We also discuss the implications for the recent activity of Sgr A*.

Sculpting the Stellar Cusp in the Galactic Center

Observations of the innermost parsec surrounding Sgr A* —the supermassive black hole in the center of our Galaxy— have revealed a diversity of structures whose existence and characteristics apparently defy the fundamental principles of dynamics. In this article, we review the challenges to the dynamics theories that have been brought forth in the past two decades by the observations of the Galactic center (GC). We outline the theoretical framework that has been developed to reconcile the discrepancies between the theoretical predictions and the observational results. In particular, we highlight the role of the recently discovered sub-parsec stellar disk in determining the dynamics and resolving the inconsistencies. We also discuss the implications for the recent activity of Sgr A*.

Kinetic energy from supernova feedback in high-resolution galaxy simulations

We describe a new method for adding a prescribed amount of kinetic energy to simulated gas modeled on a cartesian grid by directly altering grid cells’ mass and velocity in a distributed fashion. The method is explored in the context of supernova feedback in high-resolution hydrodynamic simulations of galaxy formation. In idealized tests at varying background densities and resolutions, we show convergence in behavior between models with different initial kinetic energy fractions at low densities and/or at high resolutions. We find that in high density media ($\gtrsim$ 50 cm$^{-3}$) with coarse resolution ($\gtrsim 4$ pc per cell), results are sensitive to the initial fraction of kinetic energy due to the early rapid cooling of thermal energy. We describe and test a resolution dependent scheme for adjusting this fraction that approximately replicates our high-resolution tests. We apply the method to a prompt supernova feedback model, meant to mimic Type II supernovae, in a cosmological simulation of a $10^9$ Msun halo. We find that depositing small amounts of supernova energy in kinetic form (as little as 1%) has a dramatic impact on the evolution of the system, resulting in an order of magnitude suppression of stellar mass. We discuss the distribution of stellar metallicities in the resulting system and find that while the mean metallicity is much more consistent with observations than in previous models, significant discrepancies remain that are likely due to our simplistic assumptions for the source of stellar feedback that neglect contributions from Type Ia supernovae and stellar winds.

Properties of QSO Metal Line Absorption Systems at High Redshifts: Nature and Evolution of the Absorbers and New Evidence on Escape of Ionizing Radiation from Galaxies

Using Voigt-profile-fitting procedures on Keck HIRES spectra of nine QSOs we identify 1099 CIV absorber components clumped in 201 systems outside the Lyman forest over 1.6 < z < 4.4. With associated SiIV, CII, SiII and NV where available we investigate bulk statistical and ionization properties of the components and systems and find no significant change in redshift for CIV and SiIV while CII, SiII and NV change substantially. The CIV components exhibit strong clustering but no clustering is detected for systems on scales from 150 km/s out to 50000 km/s. We conclude the clustering is due entirely to the peculiar velocities of gas present in the circumgalactic media of galaxies. Using specific combinations of ionic ratios we compare our observations with model ionization predictions for absorbers exposed to the metagalactic ionizing radiation background augmented by proximity radiation from their associated galaxies and find the generally accepted means of radiative escape by transparent channels from the internal star-forming sites is spectrally not viable for our stronger absorbers. We develop an active scenario based on runaway stars with resulting changes in the efflux of radiation that naturally enable the needed spectral convergence and in turn provide empirical indicators of morphological evolution in the associated galaxies. Together with a coexisting population of relatively compact galaxies indicated by the weaker absorbers in our sample the collective escape of radiation is sufficient to maintain the IGM ionized over the full range 1.9 < z < 4.4.

Inclination Dependence of Lyman-Alpha Properties in a Turbulent Disk Galaxy

We present simulations of Lyman-Alpha radiation transfer in an isolated disk galaxy with a turbulence sub-grid model, multi-phase interstellar medium and detailed star formation modelling. We investigate the influence of inclination on the observed Lyman-Alpha properties for different snapshots. The Lyman-alpha spectrum, equivalent width distribution and escape fractions vary significantly with the detailed morphology of the disk, leading to variations from one snapshot to another. In particular, we find that supernova-driven cavities near star-forming regions in the simulation can dominate the transmitted Lyman-alpha fraction, suggesting a variability of LAEs on the timescales of the star formation activity.

An excess of dusty starbursts related to the Spiderweb galaxy

We present APEX LABOCA 870 micron observations of the field around the high-redshift radio galaxy MRC1138-262 at z=2.16. We detect 16 submillimeter galaxies in this ~140 square arcmin bolometer map with flux densities in the range 3-11 mJy. The raw number counts indicate a density of submillimeter galaxies (SMGs) that is up to four times that of blank field surveys. Based on an exquisite multiwavelength database, including VLA 1.4 GHz radio and infrared observations, we investigate whether these sources are members of the protocluster structure at z=2.2. Using Herschel PACS+SPIRE and Spitzer MIPS photometry, we derive reliable far-infrared photometric redshifts for all sources. Follow-up VLT ISAAC and SINFONI near-infrared spectra confirm that four of these SMGs have redshifts of z=2.2. We also present evidence that another SMG in this field, detected earlier at 850 micron, has a counterpart that exhibits Halpha and CO(1-0) emission at z=2.15. Including the radio galaxy and two SMGs with far-IR photometric redshifts at z=2.2, we conclude that at least eight submm sources are part of the protocluster at z=2.16 associated with the radio galaxy MRC1138-262. We measure a star formation rate density SFRD ~1500 Msun yr^-1 Mpc^-3, four magnitudes higher than the global SFRD of blank fields at this redshift. Strikingly, these eight sources are concentrated within a region of 2 Mpc (the typical size of clusters in the local universe) and are distributed within the filaments traced by the Halpha emitters at z=2.2. This concentration of massive, dusty starbursts is not centered on the submillimeter-bright radio galaxy which could support the infalling of these sources into the cluster center. Approximately half (6/11) of the SMGs that are covered by the Halpha imaging data are associated with Halpha emitters, demonstrating the potential of tracing SMG counterparts with this population (abridged).

Structure and kinematics of the polar ring galaxies: new observations and estimation of the dark halo shape

The polar ring galaxies (PRGs) represent an interesting type of peculiar systems in which the outer matter is rotating in the plane which is roughly perpendicular to the disk of the main galaxy. Despite the long lasting study of the PRGs there is a lack of the detailed enough observational data, there are still many open questions. Among the most interesting issues there are the estimate of the flattening of the dark matter halos in these systems and the verification of the assumption that the most massive polar structures were formed by the accretion of the matter from the intergalactic filaments. The new catalog recently collected by our team using the SDSS images increased by several times the number of known PRGs. The current paper gives the overview of our latest results on the study of morphological and photometric structure of the PRGs. Using the stellar and ionized gas kinematics data based on spectral observations with the Russian 6-m telescope we estimate the dark matter halo shape in the individual galaxies.

Supermassive Black Hole Binaries: Environment and Galaxy Host Properties of PTA and eLISA sources

Supermassive black hole (BH) binaries would comprise the strongest sources of gravitational waves (GW) once they reach <<1 pc separations, for both pulsar timing arrays (PTAs) and space based (SB) detectors. While BH binaries coalescences constitute a natural outcome of the cosmological standard model and galaxy mergers, their dynamical evolution is still poorly understood and therefore their abundances at different stages. We use a dynamical model for the decay of BH binaries coupled with a cosmological simulation and semi-empirical approaches to the occupation of haloes by galaxies and BHs, in order to follow the evolution of the properties distribution of galaxies hosting BH binaries candidates to decay due to GWs emission. Our models allow us to relax simplifying hypothesis about the binaries occupation in galaxies and their mass, as well as redshift evolution. Following previously proposed electromagnetic (EM) signatures of binaries in the subpc regime, that include spectral features and variability, we model possible distributions of such signatures and also set upper limits to their lifespan. We found a bimodal distribution of hosts properties, corresponding to BH binaries suitable to be detected by PTA and the ones detectable only from space missions, as eLISA. Although it has been discussed that the peak of eLISA sources may happen at high z, we show that there must be a population of such sources in the nearby Universe that might show detectable EM signatures, representing an important laboratory for multimessenger astrophysics. We found a weak dependence of galaxy host properties on the binaries occupation, that can be traced back to the BH origin. The combination of the host correlations reported here with the expected EM signal, may be helpful to verify the presence of nearby GW candidates, and to distinguish them from ‘regular’ intrinsic AGN variability.

CARMA Large Area Star Formation Survey: Structure and Kinematics of Dense Gas in Serpens Main

We present observations of N2H+(1-0), HCO+(1-0), and HCN(1-0) toward the Serpens Main molecular cloud from the CARMA Large Area Star Formation Survey (CLASSy). We mapped 150 square arcminutes of Serpens Main with an angular resolution of 7 arcsecs. The gas emission is concentrated in two subclusters (the NW and SE subclusters). The SE subcluster has more prominent filamentary structures and more complicated kinematics compared to the NW subcluster. The majority of gas in the two subclusters has subsonic to sonic velocity dispersions. We applied a dendrogram technique with N2H+(1-0) to study the gas structures; the SE subcluster has a higher degree of hierarchy than the NW subcluster. Combining the dendrogram and line fitting analyses reveals two distinct relations: a flat relation between nonthermal velocity dispersion and size, and a positive correlation between variation in velocity centroids and size. The two relations imply a characteristic depth of 0.15 pc for the cloud. Furthermore, we have identified six filaments in the SE subcluster. These filaments have lengths of 0.2 pc and widths of 0.03 pc, which is smaller than a characteristic width of 0.1 pc suggested by Herschel observations. The filaments can be classified into two types based on their properties. The first type, located in the northeast of the SE subcluster, has larger velocity gradients, smaller masses, and nearly critical mass-per-unit-length ratios. The other type, located in the southwest of the SE subcluster, has the opposite properties. Several YSOs are formed along two filaments which have supercritical mass per unit length ratios, while filaments with nearly critical mass-per-unit-length ratios are not associated with YSOs, suggesting that stars are formed on gravitationally unstable filaments.

A Local Clue to the Reionization of the Universe

Identifying the population of galaxies that was responsible for the reionization of the universe is a long-standing quest in astronomy. We present a possible local analog that has an escape fraction of ionizing flux of 21%. Our detection confirms the existence of gaps in the neutral gas enveloping the starburst region. The candidate contains a massive yet highly compact star-forming region. The gaps are most likely created by the unusually strong winds and intense ionizing radiation produced by this extreme object. Our study also validates the indirect technique of using the residual flux in saturated low-ionization interstellar absorption-lines for identifying such leaky galaxies. Since direct detection of ionizing flux is impossible at the epoch of reionization, this is a highly valuable technique for future studies.

On the mass-metallicity relation, velocity dispersion and gravitational well depth of GRB host galaxies [Replacement]

We analyze a sample of 16 absorption systems intrinsic to long duration GRB host galaxies at $z \gtrsim 2$ for which the metallicities are known. We compare the relation between the metallicity and cold gas velocity width for this sample to that of the QSO-DLAs, and find complete agreement. We then compare the redshift evolution of the mass-metallicity relation of our sample to that of QSO-DLAs and find that also GRB hosts favour a late onset of this evolution, around a redshift of $\approx 2.6$. We compute predicted stellar masses for the GRB host galaxies using the prescription determined from QSO-DLA samples and compare the measured stellar masses for the four hosts where stellar masses have been determined from SED fits. We find excellent agreement and conclude that, on basis of all available data and tests, long duration GRB-DLA hosts and intervening QSO-DLAs are consistent with being drawn from the same underlying population. GRB host galaxies and QSO-DLAs are found to have different impact parameter distributions and we briefly discuss how this may affect statistical samples. The impact parameter distribution has two effects. First any metallicity gradient will shift the measured metallicity away from the metallicity in the centre of the galaxy, second the path of the sightline through different parts of the potential well of the dark matter halo will cause different velocity fields to be sampled. We report evidence suggesting that this second effect may have been detected.

On the mass-metallicity relation, velocity dispersion and gravitational well depth of GRB host galaxies

We analyze a sample of 16 absorption systems intrinsic to long duration GRB host galaxies at $z \gtrsim 2$ for which the metallicities are known. We compare the relation between the metallicity and cold gas velocity width for this sample to that of the QSO-DLAs, and find complete agreement. We then compare the redshift evolution of the mass-metallicity relation of our sample to that of QSO-DLAs and find that also GRB hosts favour a late onset of this evolution, around a redshift of $\approx 2.6$. We compute predicted stellar masses for the GRB host galaxies using the prescription determined from QSO-DLA samples and compare the measured stellar masses for the four hosts where stellar masses have been determined from SED fits. We find excellent agreement and conclude that, on basis of all available data and tests, long duration GRB-DLA hosts and intervening QSO-DLAs are consistent with being drawn from the same underlying population. GRB host galaxies and QSO-DLAs are found to have different impact parameter distri- butions and we briefly discuss how this may affect statistical samples. The impact parameter distribution has two effects. First any metallicity gradient will shift the measured metallicity away from the metallicity in the centre of the galaxy, second the path of the sightline through different parts of the potential well of the dark matter halo will cause different velocity fields to be sampled. We report evidence suggesting that this second effect may have been detected.

The Clustering and Halo Masses of Star Forming Galaxies at z<1

We present clustering measurements and halo masses of star forming galaxies at 0.2 < z < 1.0. After excluding AGN, we construct a sample of 22553 24 {\mu}m sources selected from 8.42 deg^2 of the Spitzer MIPS AGN and Galaxy Evolution Survey of Bo\"otes. Mid-infrared imaging allows us to observe galaxies with the highest star formation rates (SFRs), less biased by dust obscuration afflicting the optical bands. We find that the galaxies with the highest SFRs have optical colors which are redder than typical blue cloud galaxies, with many residing within the green valley. At z > 0.4 our sample is dominated by luminous infrared galaxies (LIRGs, L_TIR > 10^11 Lsun) and is comprised entirely of LIRGs and ultra-luminous infrared galaxies (ULIRGs, L_TIR > 10^12 Lsun) at z > 0.6. We observe weak clustering of r_0 = 3-6 Mpc/h for almost all of our star forming samples. We find that the clustering and halo mass depend on L_TIR at all redshifts, where galaxies with higher L_TIR (hence higher SFRs) have stronger clustering. Galaxies with the highest SFRs at each redshift typically reside within dark matter halos of M_halo ~ 10^12.9 Msun/h. This is consistent with a transitional halo mass, above which star formation is largely truncated, although we cannot exclude that ULIRGs reside within higher mass halos. By modeling the clustering evolution of halos, we connect our star forming galaxy samples to their local descendants. Most star forming galaxies at z < 1.0 are the progenitors of L < 2.5L* blue galaxies in the local universe, but star forming galaxies with the highest SFRs (L_TIR >10^11.7 Lsun) at 0.6<z<1.0 are the progenitors of early-type galaxies in denser group environments.

Evolution of galaxy stellar masses and star formation rates in the EAGLE simulations

We investigate the evolution of galaxy masses and star formation rates in the Evolution and Assembly of Galaxies and their Environment (EAGLE) simulations. These comprise a suite of hydrodynamical simulations in a $\Lambda$CDM cosmogony with subgrid models for radiative cooling, star formation, stellar mass loss, and feedback from stars and accreting black holes. The subgrid feedback was calibrated to reproduce the observed present-day galaxy stellar mass function and galaxy sizes. Here we demonstrate that the simulations reproduce the observed growth of the stellar mass density to within 20 per cent. The simulation also tracks the observed evolution of the galaxy stellar mass function out to redshift z = 7, with differences comparable to the plausible uncertainties in the interpretation of the data. Just as with observed galaxies, the specific star formation rates of simulated galaxies are bimodal, with distinct star forming and passive sequences. The specific star formation rates of star forming galaxies are typically 0.2 to 0.4 dex lower than observed, but the evolution of the rates track the observations closely. The unprecedented level of agreement between simulation and data makes EAGLE a powerful resource to understand the physical processes that govern galaxy formation.

The numerical frontier of the high-redshift Universe

The first stars are believed to have formed a few hundred million years after the big bang in so-called dark matter minihalos with masses ~10^6 M_sun. Their radiation lit up the Universe for the first time, and the supernova explosions that ended their brief lives enriched the intergalactic medium with the first heavy elements. In the wake of their feedback, the first galaxies assembled in halos with masses ~10^8 M_sun, and hosted the first normal stellar populations. In this review, I summarize the theoretical progress made in the field of high-redshift star and galaxy formation since the turn of the millennium, with an emphasis on numerical simulations. These have become the method of choice to understand the multi-physics problem posed by the simultaneous collapse of the dark matter and gas over many orders of magnitude in scale. In particular, I focus on the evolution of minihalos beyond the initial collapse of the gas, including disk fragmentation, protostellar evolution, and radiative feedback. I also discuss the influence of additional physical processes, such as magnetic fields and streaming velocities. In the second part of the review, I summarize the various feedback mechanisms exerted by the first stars, and how they affect the formation and properties of the first galaxies.

Resolving the Discrepancy of Galaxy Merger Fraction Measurements at z ~ 0 - 3

We measure the merger fraction of massive galaxies using the UltraVISTA/COSMOS $Ks$-band selected catalog, complemented with the deeper, higher resolution 3DHST+CANDELS catalog selected in the HST/WFC3 $H$-band, presenting the largest mass-complete photometric merger sample up to $z\sim3$. We find that selecting mergers using the $H_{160}$-band flux ratio leads to an increasing merger fraction with redshift, while selecting mergers using the stellar mass ratio causes a diminishing redshift dependence. Defining major and minor mergers as having stellar mass ratios of 1:1 – 4:1 and 4:1 – 10:1 respectively, the results imply $\sim$1 major and $\lesssim$1 minor merger for an average massive (log$(M_{\star}/M_{\odot}) \geqslant 10.8$) galaxy during $z=0.1-2.5$. There may be an additional $\sim 0.5(0.3)$ major (minor) merger if we use the $H$-band flux ratio selection. The observed amount of major merging alone is sufficient to explain the observed number density evolution for the very massive (log$(M_{\star}/M_{\odot}) \geqslant 11.1$) galaxies. We argue that these very massive galaxies can put on a maximum of $6\%$ of stellar mass in addition to major and minor merging, so that their number density evolution remains consistent with observations. The observed number of major and minor mergers can increase the size of a massive quiescent galaxy by a factor of two at most. This amount of merging is enough to bring the compact quiescent galaxies formed at $z>2$ to lie at $1\sigma$ below the mean of the stellar mass-size relation as measured in some works (e.g. Newman et al. 2012), but additional mechanisms are needed to fully explain the evolution, and to be consistent with works suggesting stronger evolution (e.g. van der Wel et al. 2014).

Tidal Stream Morphology as an Indicator of Dark Matter Halo Geometry: the Case of Palomar 5

This paper presents an example where the morphology of a single stellar stream can be used to rule out a specific galactic potential form without the need for velocity information. We investigate the globular cluster Palomar5 (Pal 5), which is tidally disrupting into a cold, thin stream mapped over 22 degrees on the sky with a typical width of 0.7 degrees. We generate models of this stream by fixing Pal 5′s present-day position, distance and radial velocity via observations, while allowing its proper motion to vary. In a spherical dark matter halo we easily find models that fit the observed morphology. However, no plausible Pal 5 model could be found in the triaxial potential of Law & Majewski (2010), which has been proposed to explain the properties of the Sagittarius stream. In this case, the long, thin and curved morphology of the Pal5 stream alone can be used to rule out such a potential configuration. Pal 5 like streams in this potential are either too straight, missing the curvature of the observations, or show an unusual morphology which we dub stream-fanning: a signature sensitive to the triaxiality of a potential. We conclude that the mere existence of other thin tidal streams must provide broad constraints on the orientation and shape of the dark matter halo they inhabit.

[$\alpha$/Fe] Abundances of Four Outer M 31 Halo Stars

We present alpha element to iron abundance ratios, [$\alpha$/Fe], for four stars in the outer stellar halo of the Andromeda Galaxy (M 31). The stars were identified as high-likelihood field halo stars by Gilbert et al. (2012) and lie at projected distances between 70 and 140 kpc from M 31′s center. These are the first alpha abundances measured for a halo star in a galaxy beyond the Milky Way. The stars range in metallicity between [Fe/H]= -2.2 and [Fe/H]= -1.4. The sample’s average [$\alpha$/Fe] ratio is +0.20+/-0.20. The best-fit average value is elevated above solar which is consistent with rapid chemical enrichment from Type II supernovae. The mean [$\alpha$/Fe] ratio of our M31 outer halo sample agrees (within the uncertainties) with that of Milky Way inner/outer halo stars that have a comparable range of [Fe/H].

An exploration of galaxy-galaxy lensing and galaxy clustering in the Millennium-XXL simulation

The combination of galaxy-galaxy lensing and galaxy clustering data has the potential to simultaneously constrain both the cosmological galaxy formation models. However, to fully exploit this potential one needs to understand the signals as well as their joint covariance matrix. In this paper we perform a comprehensive exploration of these ingredients, through a combination of analytic and numerical approaches. First, we derive analytic expressions for the projected galaxy correlation function and stacked tangential shear profile and their respective covariances. Second, we measure these quantities from mock galaxy catalogues derived from the Millennium-XXL simulation and semi-analytic models of galaxy formation. We find that on large scales (R>10 Mpc), the galaxy bias is roughly linear and deterministic. On smaller scales (R < 5 Mpc) the bias is a complicated function of scale and luminosity, determined by the different spatial distribution and abundance of satellite galaxies present when different magnitude cuts are applied, as well as by the dependence of the mass of haloes hosting the central galaxies on magnitude. Our theoretical model for the covariances provides a reasonably good description of the measured ones on small and large scales. However, on intermediate scales (1<R<10 Mpc), the predicted errors are ~2-3 times smaller, suggesting that the inclusion of higher-order, non-Gaussian terms in the covariance will be required for further improvements. Importantly, both our theoretical and numerical methods show that the galaxy-galaxy lensing and clustering signals are not independent from each other, but have a non-zero cross-covariance matrix with significant bin-to-bin correlations. Future surveys aiming to combine these probes must take this into account in order to obtain unbiased and realistic constraints.

Compact Binary Assembly in the First Nuclear Star Clusters and r-Process Synthesis in the Early Universe

Investigations of element abundances in the ancient and most metal deficient stars are extremely important because they serve as tests of variable nucleosynthesis pathways and can provide critical inferences of the type of stars that lived and died before them. The presence of r-process elements in a handful of carbon-enhanced metal-poor (CEMP) stars, which are assumed to be closely connected to the chemical yield from the first stars, is hard to reconcile with standard neutron star mergers. Here we show that the production rate of dynamically assembled compact binaries in high-z nuclear star clusters can attain a sufficient high value to be a potential viable source of heavy r-material in CEMP stars. The predicted frequency of such events in the early Galaxy, much lower than the frequency of Type II supernovae but with significantly higher mass ejected per event, can naturally lead to a high level of scatter of Eu as observed in CEMP stars.

Searching for gravitational wave memory bursts with the Parkes Pulsar Timing Array

Anisotropic bursts of gravitational radiation produced by events such as super-massive black hole mergers leave permanent imprints on space. Such gravitational wave "memory" (GWM) signals are, in principle, detectable through pulsar timing as sudden changes in the apparent pulse frequency of a pulsar. If an array of pulsars is monitored as a GWM signal passes over the Earth, the pulsars would simultaneously appear to change pulse frequency by an amount that varies with their sky position in a quadrupolar fashion. Here we describe a search algorithm for such events and apply the algorithm to approximately six years of data from the Parkes Pulsar Timing Array. We find no GWM events and set an upper bound on the rate for events which could have been detected. We show, using simple models of black hole coalescence rates, that this non-detection is not unexpected.

Variable Stars in Metal-Rich Globular Clusters. IV. Long Period Variables in NGC 6496

We present VI-band photometry for stars in the metal-rich globular cluster NGC 6496. Our time-series data were cadenced to search for long period variables (LPVs) over a span of nearly two years, and our variability search yielded the discovery of thirteen new variable stars, of which six are LPVs, two are suspected LPVs, and five are short period eclipsing binaries. An additional star was found in the ASAS database, and we clarify its type and period. We argue that all of the eclipsing binaries are field stars, while 5-6 of the LPVs are members of NGC 6496. We compare the period-luminosity distribution of these LPVs with those of LPVs in the Large Magellanic Cloud and 47 Tucanae, and with theoretical pulsation models. We also present a VI color magnitude diagram, display the evolutionary states of the variables, and match isochrones to determine a reddening of E(B-V) ~ 0.21 mag and apparent distance modulus of ~ 15.60 mag.

How well can cold-dark-matter substructures account for the observed radio flux-ratio anomalies? [Replacement]

Discrepancies between the observed and model-predicted radio flux ratios are seen in a number of quadruply-lensed quasars. The most favored interpretation of these anomalies is that CDM substructures present in lensing galaxies perturb the lens potentials and alter image magnifications and thus flux ratios. So far no consensus has emerged regarding whether or not the predicted CDM substructure abundance fully accounts for the lensing flux anomaly observations. Accurate modeling relies on a realistic lens sample in terms of both the lens environment and internal structures and substructures. In this paper we construct samples of generalised and specific lens potentials, to which we add (rescaled) subhalo populations from the galaxy-scale Aquarius and the cluster-scale Phoenix simulation suites. We further investigate the lensing effects from subhalos of masses several orders of magnitude below the simulation resolution limit. The resulting flux ratio distributions are compared to the currently best available sample of radio lenses. The observed anomalies in B0128+437, B1608+656 and B1933+503 are more likely to be caused by propagation effects or oversimplified lens modeling, signs of which are already seen in the data. Among the quadruple systems that have closely located image triplets/pairs, the anomalous flux ratios of MG0414+0534 can be reproduced by adding CDM subhalos to its macroscopic lens potential, with a probability of 5%-20%; for B0712+472, B1422+231, B1555+375 and B2045+265, these probabilities are only of a few percent. We hence find that CDM substructures are unlikely to be the whole reason for radio flux anomalies. We discuss other possible effects that might also be at work.

How well can cold-dark-matter substructures account for the observed radio flux-ratio anomalies?

Discrepancies between the observed and model-predicted radio flux ratios are seen in a number of quadruply-lensed quasars. The most favored interpretation of these anomalies is that CDM substructures present in lensing galaxies perturb the lens potentials and alter image magnifications and thus flux ratios. So far no consensus has emerged regarding whether or not the predicted CDM substructure abundance fully accounts for the lensing flux anomaly observations. Accurate modeling relies on a realistic lens sample in terms of both the lens environment and internal structures and substructures. In this paper we construct samples of generalised and specific lens potentials, to which we add (rescaled) subhalo populations from the galaxy-scale Aquarius and the cluster-scale Phoenix simulation suites. We further investigate the lensing effects from subhalos of masses several orders of magnitude below the simulation resolution limit. The resulting flux ratio distributions are compared to the currently best available sample of radio lenses. The observed anomalies in B0128+437, B1608+656 and B1933+503 are more likely to be caused by propagation effects or oversimplified lens modeling, signs of which are already seen in the data. Among the quadruple systems that have closely located image triplets/pairs, the anomalous flux ratios of MG0414+0534 can be reproduced by adding CDM subhalos to its macroscopic lens potential, with a probability of 5%-20%; for B0712+472, B1422+231, B1555+375 and B2045+265, these probabilities are only of a few percent. We hence find that CDM substructures are unlikely to be the whole reason for radio flux anomalies. We discuss other possible effects that might also be at work.

Orbit classification of low and high angular momentum stars

We determine the character of orbits of stars moving in the meridional plane $(R,z)$ of an axially symmetric time-independent disk galaxy model with a spherical central nucleus. In particular, we try to reveal the influence of the value of the angular momentum on the different families of orbits of stars, by monitoring how the percentage of chaotic orbits, as well as the percentages of orbits of the main regular resonant families evolve when angular momentum varies. The smaller alignment index (SALI) was computed by numerically integrating the equations of motion as well as the variational equations to extensive samples of orbits in order to distinguish safely between ordered and chaotic motion. In addition, a method based on the concept of spectral dynamics that utilizes the Fourier transform of the time series of each coordinate is used to identify the various families of regular orbits and also to recognize the secondary resonances that bifurcate from them. Our investigation takes place both in the physical $(R,z)$ and the phase $(R,\dot{R})$ space for a better understanding of the orbital properties of the system. Our numerical computations reveal that low angular momentum stars are most likely to move in chaotic orbits, while on the other hand, the vast majority of high angular momentum stars perform regular orbits.

UV spectral diagnostics for low redshift quasars: estimating physical conditions and radius of the Broad Line Region

The UV spectral range (1100 – 3000 A) contains the strongest resonance lines observed in active galactic nuclei (AGN). Analysis of UV line intensity ratios and profile shapes in quasar spectra provide diagnostics of physical and dynamical conditions in the broad line emitting region. This paper discusses properties of UV lines in type-1 AGN spectra, and how they lead an estimate of ionizing photon flux, chemical abundances, radius of the broad line emitting region and central black hole mass. These estimates are meaningfully contextualised through the 4D "eigenvector-1" (4DE1) formalism.

CCD UBVRI photometry of NGC 6811

We present the results of CCD UBVRI observations of the open cluster NGC 6811 obtained on 18th July 2012 with the 1m telescope at the T\"UB\.ITAK National Observatory (TUG). Using these photometric results, we determine the structural and astrophysical parameters of the cluster. The mean photometric uncertainties are better than 0.02 mag in the V magnitude and B-V, V-R, and V-I colour indices to about 0.03 mag for U-B among stars brighter than magnitude V=18. Cluster member stars were separated from the field stars using the Galaxia model of Sharma et al. (2011) together with other techniques. The core radius of the cluster is found to be $r_{c}$=3.60 arcmin. The astrophysical parameters were determined simultaneously via Bayesian statistics using the colour-magnitude diagrams V versus B-V, V versus V-I, V versus V-R, and V versus R-I of the cluster. The resulting most likely parameters were further confirmed using independent methods, removing any possible degeneracies. The colour excess, distance modulus, metallicity and the age of the cluster are determined simultaneously as E(B-V)=0.05$\pm$0.01 mag, $\mu=10.06\pm0.08$ mag, [M/H]=-0.10$\pm$0.01 dex and t=1.00$\pm$0.05 Gyr, respectively. Distances of five red clump stars which were found to be members of the cluster further confirm our distance estimation.

VLTI/AMBER differential interferometry of the broad-line region of the quasar 3C273

Unveiling the structure of the Broad Line Region (BLR) of AGNs is critical to understand the quasar phenomenon. Resolving a few BLRs by optical interferometry will bring decisive information to confront, complement and calibrate the reverberation mapping technique, basis of the mass-luminosity relation in quasars. BLRs are much smaller than the angular resolution of the VLT and Keck interferometers and they can be resolved only by differential interferometry very accurate measurements of differential visibility and phase as a function of wavelength. The latter yields the photocenter variation with wavelength, and constrains the size, position and velocity law of various regions of the BLR. AGNs are below the magnitude limit for spectrally resolved interferometry set by currently available fringe trackers. A new "blind" observation method and a data processing based on the accumulation of 2D Fourier power and cross spectra permitted us to obtain the first spectrally resolved interferometric observation of a BLR, on the K=10 quasar 3C273. A careful bias analysis is still in progress, but we report strong evidence that, as the baseline increases, the differential visibility decreases in the Pa-alpha line. Combined with a differential phase smaller than 3 degree, this yields an angular equivalent radius of the BLR larger than 0.4 milliarcseconds, or 1000 light days at the distance of 3C273, much larger than the reverberation mapping radius of 300 light days. Explaining the coexistence of these two different sizes, and possibly structures and mechanisms, implies very new insights into the BLR of 3C273

On the surface density of dark matter haloes

In this article, we test the conclusion of Donato et al. (2009) concerning the universality of the DM halo surface density $\mu_{0D}=\rho_0r_0$. According to our study, the dispersion of values of $\mu_{0D}$ is twice higher than that found by Donato et al. (2009). We conclude, in contrast with Donato et al. (2009), that the DM surface density and its Newtonian acceleration are not constant but correlate with the luminosity, morphological type, $(B-V)_0$ colour index, and the content of neutral hydrogen. These DM parameters are higher for more luminous systems of early types with red colour and low gas content. We also found that the correlation of DM parameters with colour index appears to be the manifestation of a stronger relation between DM halo mass and the colour of a galaxy. This finding is in agreement with cosmological simulations (Guo et al, 2011). These results leave little room for the recently claimed universality of DM column density. We also found that isolated galaxies in our sample (contained in the Analysis of the interstellar Medium of Isolated GAlaxies (AMIGA) catalogue) do not differ significantly in their value of $\mu_{0D}$ from the entire sample. Thus, since the AMIGA catalogue gives a sample of galaxies that have not interacted with a significant mass neighbour in the past 3 Gyr, the difference between the systems with low and high values of $\mu_{0D}$ is not related to the merging events during this period of time.

Simple hydrogen-bearing molecules in translucent molecular clouds

We demonstrate relations between column densities of simple molecules: CH, CH$^{+}$, H$_{2}$ and OH. The H$_{2}$, CH and OH molecules seem to occupy the same environments because of tight relations between their column densities. In contrary to this CH$^{+}$ column density does not correlate with those of other simple molecules.

Consistent system of oscillator strengths of A$^{2}\Delta$ -- X$^{2}\Pi$ (0, 0) and B$^{2}\Sigma^{-}$ -- X$^{2}\Pi$ (0, 0) bands of CH molecule [Replacement]

Detailed analysis of intensity ratios of unsaturated methylidyne (CH) A–X and B–X bands suggests consistency of the recently published oscillator strengths of A$^{2}\Delta$ — X$^{2}\Pi$ (0, 0) — 4300 \AA\ and B$^{2}\Sigma^{-}$ — X$^{2}\Pi$ (0, 0) — (3878, 3886 and 3890 \AA) bands (ie. 506, 107, 320 and 213$\times$10$^{-5}$ respectively). This result is based on extremely high S/N ratio spectra of 45 stars, acquired with three high-resolution spectrographs, situated in Chile: ESO LaSilla (HARPS), ESO Paranal (UVES) and Las Campanas (MIKE) and MAESTRO instrument situated in Northern Caucasus (Russia). The calculated methylidyne column densities, obtained using the consistent system of the oscillator strengths toward the observed targets, are given as well. We verify oscillator strengths of the CH+ A-X (0, 0) and (0, 1) bands at 4232 \AA\ and 3957 \AA\ equal to 545 and 342$\times$10$^{-5}$ respectively. We also confirm the lack of correlation between abundances of neutral CH and CH$^{+}$ which the fact demonstrates that they are originated in different environments.

Consistent system of oscillator strengths of A$^{2}\Delta$ -- X$^{2}\Pi$ (0, 0) and B$^{2}\Sigma^{-}$ -- X$^{2}\Pi$ (0, 0) bands of CH molecule

Detailed analysis of intensity ratios of unsaturated methylidyne (CH) A–X and B–X bands suggests consistency of the recently published oscillator strengths of A$^{2}\Delta$ — X$^{2}\Pi$ (0, 0) — 4300~\AA\ and B$^{2}\Sigma^{-}$ — X$^{2}\Pi$ (0, 0) — (3878, 3886 and 3890~\AA) bands (ie. 506, 107, 320 and 213$\times$10$^{-5}$ respectively). This result is based on extremely high S/N ratio spectra of 45 stars, acquired with three high-resolution spectrographs, situated in Chile: ESO LaSilla (HARPS), ESO Paranal (UVES) and Las Campanas (MIKE) and MAESTRO instrument situated in Northern Caucasus (Russia). The calculated methylidyne column densities, obtained using the consistent system of the oscillator strengths toward the observed targets, are given as well. We verify oscillator strengths of the CH+ A-X (0, 0) and (0, 1) bands at 4232~\AA\ and 3957~\AA\ equal to 545 and 342$\times$10$^{-5}$ respectively. We also confirm the lack of correlation between abundances of neutral CH and CH$^{+}$ which the fact demonstrates that they are originated in different environments.

AGN BLR structure, luminosity and mass from combined Reverberation Mapping and Optical Interferometry observations

Unveiling the structure of the Broad Line Region (BLR) of AGN is critical to understand the quasar phenomenon. Detail study of the geometry and kinematic of these objects can answer the basic questions about the central BH mass, accretion mechanism and rate, growth and evolution history. Observing the response of the BLR clouds to continuum variations, Reverberation Mapping (RM) provides size vs luminosity and mass vs luminosity relations for QSOs and Sy1 AGNs with the goal to use these objects as standard candles and mass tags. However, the RM size can receive different interpretations depending on the assumed geometry and the corresponding mass depends on an unknown geometrical factor as well on the possible confusion between local and global velocity dispersion. From RM alone, the scatter around the mean mass is as large as a factor 3. Though BLRs are expected to be much smaller than the current spatial resolution of large optical interferometers (OI), we show that differential interferometry with AMBER, GRAVITY and successors can measure the size and constrain the geometry and kinematics on a large sample of QSOs and Sy1 AGNs. AMBER and GRAVITY (K around 10.5) could be easily extended up to K equal to 13 by an external coherencer or by advanced incoherent data processing. Future VLTI instrument could reach K around 15. This opens a large AGN BLR program intended to obtain a very accurate calibration of mass, luminosity and distance measurements from RM data which will allow using many QSOs as standard candles and mass tags to study the general evolution of mass accretion in the Universe. This program is analyzed with our BLR model allowing predicting and interpreting RM and OI measures together and illustrated with the results of our observations of 3C273 with the VLTI.

Galaxy peculiar velocities in the Zone of Avoidance

Dust extinction and stellar confusion of the Milky Way hinder the detection of galaxies at low Galactic latitude, creating the so-called Zone of Avoidance (ZoA). This has hampered our understanding of the local dynamics, cosmic flow fields and the origin of the Cosmic Microwave Background dipole. The ZoA ($|b| \le 5^\circ$) is also excluded from the "whole-sky" Two Micron All-Sky Survey (2MASS) Redshift Survey (2MRS) and 2MASS Tully-Fisher Survey (2MTF). The latter aims to provide distances and peculiar velocities for all bright inclined 2MASS galaxies with $K_s^o$ $\leq 11\hbox{$.\!\!^{\rm m}$}25$. Correspondingly, knowledge about the density distribution in the ZoA remains limited to statistical interpolations. To improve on this bias we pursued two different surveys to fill in the southern and northern ZoA. These data will allow a direct measurement of galaxy peculiar velocities. In this paper we will present a newly derived optimized Tully-Fisher (TF) relation that allow accurate measures of galaxy distances and peculiar velocities for dust-obscured galaxies. We discuss further corrections for magnitudes and biases and present some preliminary results on flow fields in the southern ZoA.

Surface Brightness Profiles of Seyfert Galaxies

We built r-band surface brightness profiles by SDSS data for 16 Seyfert galaxies observed in Crimean Astrophysical Observatory. Obtained profiles can be used for finding more accurate lightcurves for these galaxies.

Extragalactic filament detection with a layer smoothing method

Filaments are clearly visible in galaxy distributions, but they are hardly detected by computer algorithms. Most methods of filament detection can be used only with numerical simulations of a large-scale structure. New simple and effective methods for the real filament detection should be developed. The method of a smoothed galaxy density field was applied in this work to SDSS data of galaxy positions. Five concentric radial layers of 100 Mpc are appropriate for filaments detection. Two methods were tested for the first layer and one more method is proposed.

 

You need to log in to vote

The blog owner requires users to be logged in to be able to vote for this post.

Alternatively, if you do not have an account yet you can create one here.

Powered by Vote It Up

^ Return to the top of page ^