arXiv subjects

N. Scoville

Publications and source records attributed to N. Scoville.

At least 73 records · Page 4Linked to original sources

arXiv2011

The Galaxy Stellar Mass Function of X-ray detected groups: environmental dependence of galaxy evolution in the COSMOS survey

We study the stellar mass distribution for galaxies in 160 X-ray detected groups of 10^13<Log(M_200/M_sun)<2x10^14 and compare it with that of galaxies in the field, to investigate the action of environment on the build up of the stellar mass. We highlight differences in the build up of the passive population in the field, which imprint features in the distribution of stellar mass of passive galaxies at Log(M/M_sun)< 10.5. The gradual diminishing of the effect when moving to groups of increasing total masses indicates that the growing influence of the environment in bound structures is responsible for the build up of a quenched component at Log(M/M_sun)< 10.5. Differently, the stellar mass distribution of star forming galaxies is similar in shape in all the environments, and can be described by a single Schechter function both in groups and in the field. Little evolution is seen up to redshift 1. Nevertheless at z=0.2-0.4 groups with M_200<6x10^13 Msun (low mass groups) tend to have a characteristic mass for star forming galaxies which is 50% higher than in higher mass groups; we interpret it as a reduced action of environmental processes in such systems. Furthermore we analyse the distribution of sSFR--Log(M) in groups and in the field, and find that groups show on average a lower sSFR (by ~0.2 dex) at z<0.8. Accordingly, we find that the fraction of star forming galaxies is increasing with redshift in all environments, but at a faster pace in the denser ones. Finally our analysis highlights that low mass groups have a higher fraction (by 50%) of the stellar mass locked in star forming galaxies than higher mass systems (i.e. 2/3 of their stellar mass).

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arXiv2011

Galaxy Pairs in COSMOS -- Merger Rate Evolution Since z=1

We present results of a statistical study of the cosmic evolution of the mass dependent major-merger rate since z=1. A stellar mass limited sample of close major-merger pairs (the CPAIR sample) was selected from the archive of the COSMOS survey. Pair fractions at different redshifts derived using the CPAIR sample and a local K-band selected pair sample show no significant variations with stellar mass. The pair fraction exhibits moderately strong cosmic evolution, with the best-fitting evolutionary index m=2.2+-0.2. The best-fitting function for the merger rate implies that galaxies with stellar mass between 1E+10 -- 3E+11 M_sun have undergone 0.5 -- 1.5 major-mergers since z=1. Our results show that, for massive galaxies at z<1, major mergers involving star forming galaxies (i.e. wet and mixed mergers) can account for the formation of both ellipticals and red quiescent galaxies (RQGs). On the other hand, major mergers cannot be responsible for the formation of most low mass ellipticals and RQGs. Our quantitative estimates indicate that major mergers have significant impact on the stellar mass assembly of the most massive galaxies, but for less massive galaxies the stellar mass assembly is dominated by the star formation. Comparison with the mass dependent (U)LIRG rates suggests that the frequency of major-merger events is comparable to or higher than that of (U)LIRGs.

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arXiv2011

The bimodality of the 10k zCOSMOS-bright galaxies up to z ~ 1: a new statistical and portable classification based on the optical galaxy properties

Our goal is to develop a new and reliable statistical method to classify galaxies from large surveys. We probe the reliability of the method by comparing it with a three-dimensional classification cube, using the same set of spectral, photometric and morphological parameters.We applied two different methods of classification to a sample of galaxies extracted from the zCOSMOS redshift survey, in the redshift range 0.5 < z < 1.3. The first method is the combination of three independent classification schemes, while the second method exploits an entirely new approach based on statistical analyses like Principal Component Analysis (PCA) and Unsupervised Fuzzy Partition (UFP) clustering method. The PCA+UFP method has been applied also to a lower redshift sample (z < 0.5), exploiting the same set of data but the spectral ones, replaced by the equivalent width of H$α$. The comparison between the two methods shows fairly good agreement on the definition on the two main clusters, the early-type and the late-type galaxies ones. Our PCA-UFP method of classification is robust, flexible and capable of identifying the two main populations of galaxies as well as the intermediate population. The intermediate galaxy population shows many of the properties of the green valley galaxies, and constitutes a more coherent and homogeneous population. The fairly large redshift range of the studied sample allows us to behold the downsizing effect: galaxies with masses of the order of $3\cdot 10^{10}$ Msun mainly are found in transition from the late type to the early type group at $z>0.5$, while galaxies with lower masses - of the order of $10^{10}$ Msun - are in transition at later epochs; galaxies with $M <10^{10}$ Msun did not begin their transition yet, while galaxies with very large masses ($M > 5\cdot 10^{10}$ Msun) mostly completed their transition before $z\sim 1$.

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arXiv2011

Black hole accretion and host galaxies of obscured quasars in XMM-COSMOS

We explore the connection between black hole growth at the center of obscured quasars selected from the XMM-COSMOS survey and the physical properties of their host galaxies. We study a bolometric regime ( 8 x 10^45 erg/s) where several theoretical models invoke major galaxy mergers as the main fueling channel for black hole accretion. We confirm that obscured quasars mainly reside in massive galaxies (Mstar>10^10 Msun) and that the fraction of galaxies hosting such powerful quasars monotonically increases with the stellar mass. We stress the limitation of the use of rest-frame color-magnitude diagrams as a diagnostic tool for studying galaxy evolution and inferring the influence that AGN activity can have on such a process. We instead use the correlation between star-formation rate and stellar mass found for star-forming galaxies to discuss the physical properties of the hosts. We find that at z ~1, ~62% of Type-2 QSOs hosts are actively forming stars and that their rates are comparable to those measured for normal star-forming galaxies. The fraction of star-forming hosts increases with redshift: ~71% at z ~2, and 100% at z ~3. We also find that the the evolution from z ~1 to z ~3 of the specific star-formation rate of the Type-2 QSO hosts is in excellent agreement with that measured for star-forming galaxies. From the morphological analysis, we conclude that most of the objects are bulge-dominated galaxies, and that only a few of them exhibit signs of recent mergers or disks. Finally, bulge-dominated galaxies tend to host Type-2 QSOs with low Eddington ratios (lambda<0.1), while disk-dominated or merging galaxies have at their centers BHs accreting at high Eddington ratios (lambda > 0.1).

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arXiv2011

Dissecting Photometric redshift for Active Galactic Nuclei using XMM- and Chandra-COSMOS samples

With this paper, we release accurate photometric redshifts for 1692 counterparts to Chandra sources in the central square degree of the COSMOS field. The availability of a large training set of spectroscopic redshifts that extends to faint magnitudes enabled photometric redshifts comparable to the highest quality results presently available for normal galaxies. We demonstrate that morphologically extended, faint X-ray sources without optical variability are more accurately described by a library of normal galaxies (corrected for emission lines) than by AGN-dominated templates, even if these sources have AGN-like X-ray luminosities. Preselecting the library on the bases of the source properties allowed us to reach an accuracy sigma_(Delta z/(1+z_spec)) \sim0.015 with a fraction of outliers of 5.8% for the entire Chandra-COSMOS sample. In addition, we release revised photometric redshifts for the 1735 optical counterparts of the XMM-detected sources over the entire 2 sq. deg.of COSMOS. For 248 sources, our updated photometric redshift differs from the previous release by Delta z>0.2. These changes are predominantly due to the inclusion of newly available deep H-band photometry H_AB=24 mag. We illustrate once again the importance of a spectroscopic training sample and how an assumption about the nature of a source together with the number and the depth of the available bands influence the accuracy of the photometric redshifts determined for AGN. These considerations should be kept in mind when defining the observational strategies of upcoming large surveys targeting AGN, such as eROSITA at X-ray energies and ASKAP/EMU in the radio band.

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arXiv2011

On the occupation of X-ray selected galaxy groups by radio AGN since z=1.3

Previous clustering analysis of low-power radio AGN has indicated that they preferentially live in massive groups. The X-ray surveys of the COSMOS field have achieved a sensitivity at which these groups are directly detected out to z=1.3. Making use of Chandra-, XMM- and VLA-COSMOS surveys we identify radio AGN members (10**23.6 < L_1.4GHz/(W/Hz) < 10**25) of galaxy groups (10**13.2 < M_200/M_sun < 10**14.4; 0.1<z<1.3) and study i) the radio AGN -- X-ray group occupation statistics as a function of group mass, and ii) the distribution of radio AGN within the groups. We find that radio AGN are preferentially associated with galaxies close to the center (< 0.2r_200). Compared to our control sample of group members matched in stellar mass and color to the radio AGN host galaxies, we find a significant enhancement of radio AGN activity associated with 10**13.6 < M_200/M_sun < 10**14 halos. We present the first direct measurement of the halo occupation distribution (HOD) for radio AGN, based on the total mass function of galaxy groups hosting radio AGN. Our results suggest a possible deviation from the usually assumed power law HOD model. We also find an overall increase of the fraction of radio AGN in galaxy groups (<1r_200), relative to that in all environments.

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arXiv2011

Dust-obscured star formation and the contribution of galaxies escaping UV/optical color selections at z~2

A substantial fraction of the stellar mass growth across cosmic time occurred within dust-enshrouded environments. Yet, the exact amount of star-forming activity that took place in high-redshift dusty galaxies currently missed by optical surveys has been barely explored. Using the Spitzer observations of COSMOS we determined the fraction of luminous star-forming galaxies at 1.5<z<3 escaping the traditional color selection techniques because of dust extinction, as well as their contribution to the cosmic star formation density at high redshift. We find that the BzK criterion offers an almost complete (~90%) identification of the 24mic sources at 1.4<z<2.5, while the BM/BX criterion miss 50% of the MIPS population. Similarly the criterion based on the presence of a stellar bump in massive sources (so-called "IRAC peakers") miss up to 40% of the IR luminosity density and only 25% of the IR energy density at z~2 is produced by Optically-Faint IR-bright galaxies selected based on their extreme mid-IR to optical flux ratios. We conclude that color selections of distant star-forming galaxies must be used with lots of care given the substantial bias they can suffer. In particular, the effect of dust extinction strongly impacts the completeness of identifications at the bright end of the bolometric luminosity function, which implies large and uncertain extrapolations to account for the contribution of dusty galaxies missed by these selections. In the context of forthcoming facilities that will operate at long wavelengths (e.g., $JWST$, ALMA, SAFARI, EVLA, SKA), this emphasizes the importance of minimizing the extinction biases when probing the activity of star formation in the early Universe.

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arXiv2011

AzTEC millimeter survey of the COSMOS field - III. Source catalog over 0.72 sq. deg. and plausible boosting by large-scale structure

We present a 0.72 sq. deg. contiguous 1.1mm survey in the central area of the COSMOS field carried out to a 1sigma ~ 1.26 mJy/beam depth with the AzTEC camera mounted on the 10m Atacama Submillimeter Telescope Experiment (ASTE). We have uncovered 189 candidate sources at a signal-to-noise ratio S/N >= 3.5, out of which 129, with S/N >= 4, can be considered to have little chance of being spurious (< 2 per cent). We present the number counts derived with this survey, which show a significant excess of sources when compared to the number counts derived from the ~0.5 sq. deg. area sampled at similar depths in the Scuba HAlf Degree Extragalactic Survey (SHADES, Austermann et al. 2010). They are, however, consistent with those derived from fields that were considered too small to characterize the overall blank-field population. We identify differences to be more significant in the S > 5 mJy regime, and demonstrate that these excesses in number counts are related to the areas where galaxies at redshifts z < 1.1 are more densely clustered. The positions of optical-IR galaxies in the redshift interval 0.6 < z < 0.75 are the ones that show the strongest correlation with the positions of the 1.1mm bright population (S > 5 mJy), a result which does not depend exclusively on the presence of rich clusters within the survey sampled area. The most likely explanation for the observed excess in number counts at 1.1mm is galaxy-galaxy and galaxy-group lensing at moderate amplification levels, that increases in amplitude as one samples larger and larger flux densities. This effect should also be detectable in other high redshift populations.

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arXiv2011

CO(1-0) imaging of M51 with CARMA and NRO45

We report the CO(J=1-0) observations of M51 using both the Combined Array for Research in Millimeter Astronomy (CARMA) and the Nobeyama 45m telescope (NRO45). We describe a procedure for the combination of interferometer and single-dish data. In particular, we discuss (1) the joint imaging and deconvolution of heterogeneous data, (2) the weighting scheme based on the root-mean-square (RMS) noise in the maps, (3) the sensitivity and uv-coverage requirements, and (4) the flux recovery of a combined map. We generate visibilities from the single-dish map and calculate the noise of each visibility based on the RMS noise. Our weighting scheme, though it is applied to discrete visibilities in this paper, is applicable to grids in uv-space, and this scheme may advance in future software development. For a realistic amount of observing time, the sensitivities of the NRO45 and CARMA visibility data sets are best matched by using the single dish baselines only up to 4-6 kilo-lambda (about 1/4-1/3 of the dish diameter). The synthesized beam size is determined to conserve the flux between synthesized beam and convolution beam. The superior uv-coverage provided by the combination of CARMA long baseline data with 15 antennas and NRO45 short spacing data results in the high image fidelity, which is evidenced by the excellent overlap between even the faint CO emission and dust lanes in an optical HST image and PAH emission in an Spitzer 8 micron image.

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arXiv2011

On the evolution of environmental and mass properties of strong lens galaxies in COSMOS

Among the 100 strong lens candidates found in the COSMOS field, 20 with redshifts in the range [0.34,1.13], feature multiple images of background sources. Using the multi-wavelength coverage of the field and its spectroscopic follow-up, we characterize the evolution with redshift of the environment and of the dark-matter (DM) fraction of the lens galaxies. We present new redshift of the strong lens candidates. The lens environment is characterized by the projected 10 closest galaxies around each lens and by the number of galaxies with a projected distance less than 1Mpc at the lens galaxy redshift. In both cases, we perform similar measurements on a control sample of twin non-lens early type galaxies (ETGs). In addition, we identify group members and field galaxies in the X-ray and optical catalogs of galaxy groups. From those catalogs, we measure the external shear contribution at the lens galaxy positions. The systems are then modeled using a SIE plus the external shear due to the groups. We observe that the average stellar mass of lens galaxies increases with z and that the environment of lens galaxies is compatible with that of the twins. During the lens modeling, we notice that, when let free, the external shear points in a direction which is the mean direction of the external shear due to groups and of the closest galaxy to the lens. We notice that the DM fraction of the lens galaxies within the Einstein radius decreases as the redshift increases. Given these, we conclude that, while the environment of lens galaxies is compatible with that of non-lens ETGS, their mass properties evolves significantly with redshift: it is still not clear whether this advocates in favor of a stronger lensing bias toward massive objects at high redshift or is simply representative of the high proportion of massive and high stellar density galaxies at high redshift.

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arXiv2010

Tracking the impact of environment on the Galaxy Stellar Mass Function up to z~1 in the 10k zCOSMOS sample

We study the impact of the environment on the evolution of galaxies in the zCOSMOS 10k sample in the redshift range 0.1<z<1.0 over an area of ~1.5 deg2. The considered sample of secure spectroscopic redshifts contains about 8500 galaxies, with their stellar masses estimated by SED fitting of the multiwavelength optical to NIR photometry. The evolution of the galaxy stellar mass function (GSMF) in high and low density regions provides a tool to study the mass assembly evolution in different environments; moreover, the contributions to the GSMF from different galaxy types, as defined by their SEDs and their morphologies, can be quantified. At redshift z~1, the GSMF is only slightly dependent on environment, but at lower redshifts the shapes of the GSMFs in high- and low-density environments become extremely different, with high density regions exhibiting a marked bimodality. As a result, we infer that galaxy evolution depends on both the stellar mass and the environment, the latter setting the probability of a galaxy to have a given mass: all the galaxy properties related to the stellar mass show a dependence on environment, reflecting the difference observed in the mass functions. The shapes of the GSMFs of early- and late-type galaxies are almost identical for the extremes of the density contrast we consider. The evolution toward z=0 of the mass at which the early- and late-type GSMFs match each other is more rapid in high density environments. The comparison of the observed GSMFs to the same quantities derived from a set of mock catalogues shows that blue galaxies in sparse environments are overproduced in the semi-analytical models at intermediate and high masses, because of a deficit of star formation suppression, while at z<0.5 an excess of red galaxies is present in dense environments at intermediate and low masses, because of the overquenching of satellites. ABRIDGED

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arXiv2010

Mass and environment as drivers of galaxy evolution in SDSS and zCOSMOS and the origin of the Schechter function

We explore the inter-relationships between mass, star-formation rate and environment in the SDSS, zCOSMOS and other surveys. The differential effects of mass and environment are completely separable to z ~ 1, indicating that two distinct processes are operating, "mass-quenching" and "environment-quenching". Environment-quenching, at fixed over-density, evidently does not change with epoch to z ~ 1, suggesting that it occurs as large-scale structure develops in the Universe. The observed constancy of the mass-function shape for star-forming galaxies, demands that the mass-quenching of galaxies around and above M*, must be proportional to their star-formation rates at all z < 2. We postulate that this simple mass-quenching law also holds over a much broader range of stellar mass and epoch. These two simple quenching processes, plus some additional quenching due to merging, then naturally produce (a) a quasi-static Schechter mass function for star-forming galaxies with a value of M* that is set by the proportionality between the star-formation and mass-quenching rates, (b) a double Schechter function for passive galaxies with two components: the dominant one is produced by mass-quenching and has exactly the same M* as the star-forming galaxies but an alpha shallower by +1, while the other is produced by environment effects and has the same M* and alpha as the star-forming galaxies, and is larger in high density environments. Subsequent merging of quenched galaxies modifies these predictions somewhat in the denser environments, slightly increasing M* and making alpha more negative. All of these detailed quantitative relationships between the Schechter parameters are indeed seen in the SDSS, lending strong support to our simple empirically-based model. The model naturally produces for passive galaxies the "anti-hierarchical" run of mean ages and alpha-element abundances with mass.

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arXiv2010

zCOSMOS 10k-bright spectroscopic sample: exploring mass and environment dependence in early-type galaxies

We present the analysis of the U-V rest-frame color distribution and some spectral features as a function of mass and environment for two sample of early-type galaxies up to z=1 extracted from the zCOSMOS spectroscopic survey. The first sample ("red galaxies") is defined with a photometric classification, while the second ("ETGs") by combining morphological, photometric, and spectroscopic properties to obtain a more reliable sample. We find that the color distribution of red galaxies is not strongly dependent on environment for all mass bins, with galaxies in overdense regions redder than galaxies in underdense regions with a difference of 0.027\pm0.008 mag. The dependence on mass is far more significant, with average colors of massive galaxies redder by 0.093\pm0.007 mag than low-mass galaxies throughout the entire redshift range. We study the color-mass relation, finding a mean slope 0.12\pm0.005, while the color-environment relation is flatter, with a slope always smaller than 0.04. The spectral analysis that we perform on our ETGs sample is in good agreement with our photometric results: we find for D4000 a dependence on mass between high and low-mass galaxies, and a much weaker dependence on environment (respectively a difference of of 0.11\pm0.02 and of 0.05\pm0.02); for the equivalent width of Hδwe measure a difference of 0.28\pm0.08 Åacross the same mass range and no significant dependence on environment.By analyzing the lookback time of early-type galaxies, we support the possibility of a downsizing scenario, in which massive galaxies with a stronger D4000 and an almost constant equivalent width of $Hδ$ formed their mass at higher redshift than lower mass ones. We also conclude that the main driver of galaxy evolution is the galaxy mass, the environment playing a subdominant role.

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arXiv2010

The zCOSMOS 10k-sample: the role of galaxy stellar mass in the colour-density relation up to z=1

[Abridged] With the first 10000 spectra of the flux limited zCOSMOS sample (I<=22.5) we study the evolution of environmental effects on galaxy properties since z=1.0, and disentangle the dependence among galaxy colour, stellar mass and local density (3D local density contrast `delta', computed with the 5th nearest neighbour approach). We confirm that within a luminosity-limited sample (M_B<=-20.5-z) the fraction of red (U-B>=1) galaxies 'f_red' depends on delta at least up to z=1, with red galaxies residing mainly in high densities. This trend weakens for increasing z, and it is mirrored by the behaviour of the fraction of galaxies with D4000A break >=1.4. We also find that up to z=1 the fraction of galaxies with log(EW[OII]) >=1.15 is higher for lower delta, and also this dependence weakens for increasing z. Given the triple dependence among galaxy colours, stellar mass and delta, the colour-delta relation found in the luminosity-selected sample can be due to the broad range of stellar masses. Thus, we fix the stellar mass and we find that in this case the colour-delta relation is flat up to z=1 for galaxies with log(M/M_sun)>=10.7. This means that for these masses the colour-delta relation found in a luminosity-selected sample is the result of the combined colour-mass and mass-delta relations. In contrast, we find that for 0.1<=z<=0.5 and log(M/M_sun)<=10.7 'f_red' depends on delta even at fixed mass. In these mass and z ranges, environment affects directly also galaxy colours. We suggest a scenario in which the colour depends primarily on stellar mass, but for relatively low mass galaxies the local density modulates this dependence. These galaxies formed more recently, in an epoch when evolved structures were already in place, and their longer SFH allowed environment-driven physical processes to operate during longer periods of time.

astro-ph.CO↗

arXiv2010

The Rise and Fall of Passive Disk Galaxies: Morphological Evolution Along the Red Sequence Revealed by COSMOS

The increasing abundance of passive "red-sequence" galaxies since z=1-2 is mirrored by a coincident rise in the number of galaxies with spheroidal morphologies. In this paper, however, we show that in detail the correspondence between galaxy morphology and color is not perfect, providing insight into the physical origin of this evolution. Using the COSMOS survey, we study a significant population of red sequence galaxies with disk-like morphologies. These passive disks typically have Sa-Sb morphological types with large bulges, but they are not confined to dense environments. They represent nearly one-half of all red-sequence galaxies and dominate at lower masses (log Mstar < 10) where they are increasingly disk-dominated. As a function of time, the abundance of passive disks with log Mstar < 11 increases, but not as fast as red-sequence spheroidals in the same mass range. At higher mass, the passive disk population has declined since z~1, likely because they transform into spheroidals. We estimate that as much as 60% of galaxies transitioning onto the red sequence evolve through a passive disk phase. The origin of passive disks therefore has broad implications for understanding how star formation shuts down. Because passive disks tend to be more bulge-dominated than their star-forming counterparts, a simple fading of blue disks does not fully explain their origin. We explore several more sophisticated explanations, including environmental effects, internal stabilization, and disk regrowth during gas-rich mergers. While previous work has sought to explain color and morphological transformations with a single process, these observations open the way to new insight by highlighting the fact that galaxy evolution may actually proceed through several separate stages.

astro-ph.CO↗

arXiv2010

Obscured star-formation and environment in the COSMOS field

We investigate the effects of the environment on star-formation in a sample of massive luminous and ultra-luminous infrared galaxies (LIRGs and ULIRGs) with S(24 micron)>80 uJy and i+<24 in the COSMOS field. We exploit the accurate photometric redshifts in COSMOS to characterize the galaxy environment and study the evolution of the fraction of LIRGs and ULIRGs in different environments in the redshift range z=0.3-1.2 and in bins of stellar mass. We find that the environment plays a role in the star formation processes and evolution of LIRGs and ULIRGs. We find an overall increase of the ULIRG+LIRG fraction in an optically-selected sample with increasing redshift, as expected from the evolution of the star formation rate density. We find that the ULIRG+LIRG fraction decreases with increasing density up to z~1, and that the dependence on density flattens with increasing redshift. We do not observe the reversal of the star-formation rate density relation up to z=1 in massive LIRGs and ULIRGs, suggesting that such reversal might occur at higher redshift in this infrared luminosity range.

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arXiv2010

Understanding the shape of the galaxy two-point correlation function at z~1 in the COSMOS field

We investigate how the shape of the galaxy two-point correlation function as measured in the zCOSMOS survey depends on local environment, quantified in terms of the density contrast on scales of 5 Mpc/h. We show that the flat shape previously observed at redshifts between z=0.6 and z=1 can be explained by this volume being simply 10% over-abundant in high-density environments, with respect to a Universal density probability distribution function. When galaxies corresponding to the top 10% tail of the distribution are excluded, the measured w_p(r_p) steepens and becomes indistinguishable from LCDM predictions on all scales. This is the same effect recognised by Abbas & Sheth in the SDSS data at z~0 and explained as a natural consequence of halo-environment correlations in a hierarchical scenario. Galaxies living in high-density regions trace dark matter halos with typically higher masses, which are more correlated. If the density probability distribution function of the sample is particularly rich in high-density regions because of the variance introduced by its finite size, this produces a distorted two-point correlation function. We argue that this is the dominant effect responsible for the observed "peculiar" clustering in the COSMOS field.

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arXiv2010

Bars in early- and late-type disks in COSMOS

We investigate the (large-scale) bar fraction in a mass-complete sample of M > 10^10.5 Msun disk galaxies at 0.2 < z < 0.6 in the COSMOS field. The fraction of barred disks strongly depends on mass, disk morphology, and specific star formation rate (SSFR). At intermediate stellar mass (10^10.5 < M < 10^11 Msun) the bar fraction in early-type disks is much higher, at all redshifts, by a factor ~2, than that in late-type disks. This trend is reversed at higher stellar mass (M > 10^11 Msun), where the fraction of bars in early-type disks becomes significantly lower, at all redshifts, than that in late-type disks. The bar fractions for galaxies with low and high SSFRs closely follow those of the morphologically-selected early-type and late-type populations, respectively. This indicates a close correspondence between morphology and SSFR in disk galaxies at these earlier epochs. Interestingly, the total bar fraction in 10^10.5 < M < 10^11 Msun disks is built up by a factor of ~2 over the redshift interval explored, while for M > 10^11 Msun disks it remains roughly constant. This indicates that, already by z ~ 0.6, spectral and morphological transformations in the most massive disk galaxies have largely converged to the familiar Hubble sequence that we observe in the local Universe, while for intermediate mass disks this convergence is ongoing until at least z ~ 0.2. Moreover, these results highlight the importance of employing mass-limited samples for quantifying the evolution of barred galaxies. Finally, the evolution of the barred galaxy populations investigated does not depend on the large-scale environmental density (at least, on the scales which can be probed with the available photometric redshifts).

astro-ph.CO↗