Galaxy morphology and evolution from SWAN Adaptive Optics imaging

We present the results from adaptive optics (AO) assisted imaging in the Ks band of an area of 15 arcmin^2 for SWAN (Survey of a Wide Area with NACO). We derive the high resolution near-IR morphology of ~400 galaxies up to Ks~23.5 in the first 21 SWAN fields around bright guide stars, carefully taking into account the survey selection effects and using an accurate treatment of the anisoplanatic AO PSF. The detected galaxies are sorted into two morphological classes according to their Sersic index. The extracted morphological properties and number counts of the galaxies are compared with the predictions of different galaxy formation and evolution models, both for the whole galaxy population and separately for late-type and early-type galaxies. This is one of the first times such a comparison has been done in the near-IR, as AO observations and accurate PSF modeling are needed to obtain reliable morphological classification of faint field galaxies at these wavelengths. For early-type galaxies we find that a pure luminosity evolution model, without evidence for relevant number and size evolution, better reproduces the observed properties of our Ks-selected sample than current semi-analytic models based on the hierarchical picture of galaxy formation. In particular, we find that the observed flattening of elliptical galaxy counts at Ks~20 is quantitatively in good agreement with the prediction of the pure luminosity evolution model that was calculated prior to the observation. For late-type galaxies, while both models are able to reproduce the number counts, we find some hints of a possible size growth. These results demonstrate the unique power of AO observations to derive high resolution details of faint galaxies' morphology in the near-IR and drive studies of galaxy evolution.Comment: 15 pages, 10 figures. A&A, in press. Final version with corrected typo

Cosmic Star Formation: Constraints on the Galaxy Formation Models

We study the evolution of the cosmic star formation by computing the luminosity density (LD) in the UV, B, J, and K bands, and the stellar mass density (MD) of galaxies in two reference models of galaxy evolution: the pure luminosity evolution (PLE) model developed by Calura & Matteucci (2003) and the semi-analytical model (SAM) of hierarchical galaxy formation by Menci et al. (2002). The former includes a detailed description of the chemical evolution of galaxies of different morphological types with no density evolution; the latter includes the merging histories of the galactic DM haloes, as predicted by the hierarchical clustering scenario, but it does not contain morphological classification nor chemical evolution. We find that at z< 1.5 both models are consistent with the available data on the LD of galaxies in all the considered bands. At high z, the LDs predicted in the PLE model show a peak due to the formation of ellipticals, whereas the SAM predicts a gradual decrease of the star formation and of the LD for z> 2.5. At such redshifts the PLE predictions tend to overestimate the present data in the B band whereas the SAM tends to underestimate the observed UV LD. As for the stellar MD, the PLE picture predicts that nearly 50% and 85% of the present stellar mass are in place at z=4 and z=1, respectively. According to the SAM, 50% and 60% of the present stellar mass are in place at z=1.2 and z=1, respectively. Both predictions fit the observed MD up to z=1. At z>1, the PLE model and the SAM tend to overestimate and underestimate the observed values, respectively. We discuss the origin of the above model results, and the role of observational uncertainties (such as dust extinction) in comparing models with observations.Comment: 14 pages, accepted for publication in MNRA

Morphological studies of the Spitzer Wide-Area Infrared Extragalactic survey galaxy population in the UGC 10214 Hubble space telescope/advanced camera for surveys field

We present the results of a morphological analysis of a small subset of the Spitzer Wide-Area Infrared Extragalactic survey (SWIRE) galaxy population. The analysis is based on public Advanced Camera for Surveys (ACS) data taken inside the SWIRE N1 field, which are the deepest optical high-resolution imaging available within the SWIRE fields as of today. Our reference sample includes 156 galaxies detected by both ACS and SWIRE. Among the various galaxy morphologies, we disentangle two main classes, spheroids (or bulge-dominated galaxies) and disc-dominated ones, for which we compute the number counts as a function of flux. We then limit our sample to objects with Infrared Array Camera (IRAC) fluxes brighter than 10 μJy, estimated ~90 per cent completeness limit of the SWIRE catalogues, and compare the observed counts to model predictions. We find that the observed counts of the spheroidal population agree with the expectations of a hierarchical model while a monolithic scenario predicts steeper counts. Both scenarios, however, underpredict the number of late-type galaxies. These observations show that the large majority (close to 80 per cent) of the 3.6- and 4.5-μm galaxy population, even at these moderately faint fluxes, is dominated by spiral and irregular galaxies or mergers

Multivariate Approaches to Classification in Extragalactic Astronomy

Clustering objects into synthetic groups is a natural activity of any science. Astrophysics is not an exception and is now facing a deluge of data. For galaxies, the one-century old Hubble classification and the Hubble tuning fork are still largely in use, together with numerous mono-or bivariate classifications most often made by eye. However, a classification must be driven by the data, and sophisticated multivariate statistical tools are used more and more often. In this paper we review these different approaches in order to situate them in the general context of unsupervised and supervised learning. We insist on the astrophysical outcomes of these studies to show that multivariate analyses provide an obvious path toward a renewal of our classification of galaxies and are invaluable tools to investigate the physics and evolution of galaxies.Comment: Open Access paper. http://www.frontiersin.org/milky\_way\_and\_galaxies/10.3389/fspas.2015.00003/abstract\&gt;. \&lt;10.3389/fspas.2015.00003 \&g

zCOSMOS – 10k-bright spectroscopic sample : The bimodality in the galaxy stellar mass function: exploring its evolution with redshift

We present the galaxy stellar mass function (GSMF) to redshift z ≃ 1, based on the analysis of about 8500 galaxies with I < 22.5 (AB mag) over 1.4 deg^2, which are part of the zCOSMOS-bright 10k spectroscopic sample. We investigate the total GSMF, as well as the contributions of early- and late-type galaxies (ETGs and LTGs, respectively), defined by different criteria (broad-band spectral energy distribution, morphology, spectral properties, or star formation activities). We unveil a galaxy bimodality in the global GSMF, whose shape is more accurately represented by 2 Schechter functions, one linked to the ETG and the other to the LTG populations. For the global population, we confirm a mass-dependent evolution (“mass-assembly downsizing”), i.e., galaxy number density increases with cosmic time by a factor of two between z = 1 and z = 0 for intermediate-to-low mass (log(M/M_⊙) ~ 10.5) galaxies but less than 15% for log(M/M_⊙) > 11.We find that the GSMF evolution at intermediate-to- low values of M(log(M/M_⊙) < 10.6) is mostly explained by the growth in stellar mass driven by smoothly decreasing star formation activities, despite the redder colours predicted in particular at low redshift. The low residual evolution is consistent, on average, with ~0.16 merger per galaxy per Gyr (of which fewer than 0.1 are major), with a hint of a decrease with cosmic time but not a clear dependence on the mass. From the analysis of different galaxy types, we find that ETGs, regardless of the classification method, increase in number density with cosmic time more rapidly with decreasing M, i.e., follow a top-down building history, with a median “building redshift” increasing with mass (z > 1 for log(M/M_⊙) > 11), in contrast to hierarchical model predictions. For LTGs, we find that the number density of blue or spiral galaxies with log(M/M_⊙) > 10 remains almost constant with cosmic time from z ~ 1. Instead, the most extreme population of star-forming galaxies (with high specific star formation), at intermediate/high-mass, rapidly decreases in number density with cosmic time. Our data can be interpreted as a combination of different effects. Firstly, we suggest a transformation, driven mainly by SFH, from blue, active, spiral galaxies of intermediate mass to blue quiescent and subsequently (1−2 Gyr after) red, passive types of low specific star formation. We find an indication that the complete morphological transformation, probably driven by dynamical processes, into red spheroidal galaxies, occurred on longer timescales or followed after 1−2 Gyr. A continuous replacement of blue galaxies is expected to be accomplished by low-mass active spirals increasing their stellar mass. We estimate the growth rate in number and mass density of the red galaxies at different redshifts and masses. The corresponding fraction of blue galaxies that, at any given time, is transforming into red galaxies per Gyr, due to the quenching of their SFR, is on average ~25% for log(M/M_⊙) < 11. We conclude that the build-up of galaxies and in particular of ETGs follows the same downsizing trend with mass (i.e. occurs earlier for high-mass galaxies) as the formation of their stars and follows the converse of the trend predicted by current SAMs. In this scenario, we expect there to be a negligible evolution of the galaxy baryonic mass function (GBMF) for the global population at all masses and a decrease with cosmic time in the GBMF for the blue galaxy population at intermediate-high masses

First phylogenetic analyses of galaxy evolution

The Hubble tuning fork diagram, based on morphology, has always been the preferred scheme for classification of galaxies and is still the only one originally built from historical/evolutionary relationships. At the opposite, biologists have long taken into account the parenthood links of living entities for classification purposes. Assuming branching evolution of galaxies as a "descent with modification", we show that the concepts and tools of phylogenetic systematics widely used in biology can be heuristically transposed to the case of galaxies. This approach that we call "astrocladistics" has been first applied to Dwarf Galaxies of the Local Group and provides the first evolutionary galaxy tree. The cladogram is sufficiently solid to support the existence of a hierarchical organization in the diversity of galaxies, making it possible to track ancestral types of galaxies. We also find that morphology is a summary of more fundamental properties. Astrocladistics applied to cosmology simulated galaxies can, unsurprisingly, reconstruct the correct "genealogy". It reveals evolutionary lineages, divergences from common ancestors, character evolution behaviours and shows how mergers organize galaxy diversity. Application to real normal galaxies is in progress. Astrocladistics opens a new way to analyse galaxy evolution and a path towards a new systematics of galaxies