ABSTRACT
We investigate the contribution of clumps and satellites to the galaxy mass assembly. We analysed spatially resolved HubbleSpace Telescope observations (imaging and slitless spectroscopy) of ...53 star-forming galaxies at z ∼ 1–3. We created continuum and emission line maps and pinpointed residual ‘blobs’ detected after subtracting the galaxy disc. Those were separated into compact (unresolved) and extended (resolved) components. Extended components have sizes ∼2 kpc and comparable stellar mass and age as the galaxy discs, whereas the compact components are 1.5 dex less massive and 0.4 dex younger than the discs. Furthermore, the extended blobs are typically found at larger distances from the galaxy barycentre than the compact ones. Prompted by these observations and by the comparison with simulations, we suggest that compact blobs are in situ formed clumps, whereas the extended ones are accreting satellites. Clumps and satellites enclose, respectively, ∼20 per cent and ≲80 per cent of the galaxy stellar mass, ∼30 per cent and ∼20 per cent of its star formation rate. Considering the compact blobs, we statistically estimated that massive clumps (M⋆ ≳ 109 M⊙) have lifetimes of ∼650 Myr, and the less massive ones (108 < M⋆ < 109 M⊙) of ∼145 Myr. This supports simulations predicting long-lived clumps (lifetime ≳ 100 Myr). Finally, ≲30 per cent (13 per cent) of our sample galaxies are undergoing single (multiple) merger(s), they have a projected separation ≲10 kpc, and the typical mass ratio of our satellites is 1:5 (but ranges between 1:10 and 1:1), in agreement with literature results for close pair galaxies.
We have obtained spectroscopic confirmation with Hubble Space Telescope WFC3/G141 of a first sizeable sample of nine quiescent galaxies at 2.4 < z < 3.3. Their average near-UV/optical rest-frame ...spectrum is characterized by low attenuation (AV ∼ 0.6 mag) and a strong Balmer break, larger than the 4000 break, corresponding to a fairly young age of ∼300 Myr. This formally classifies a substantial fraction of classically selected quiescent galaxies at z ∼ 3 as post-starbursts, marking their convergence to the quenching epoch. The rapid spectral evolution with respect to z ∼ 1.5 quiescent galaxies is not matched by an increase of residual star formation, as judged from the weak detection of O iiλ3727 emission, pointing to a flattening of the steep increase in gas fractions previously seen from z ∼ 0 to 1.8. However, radio 3 GHz stacked emission implies either much stronger dust-obscured star formation or substantial further evolution in radio-mode AGN activity with respect to z ∼ 1.5.
We present deep Hubble Space Telescope Wide Field Camera 3 (HST/WFC3) slitless spectroscopic observations of the distant cluster Cl J1449+0856. These cover a single pointing with 18 orbits of G141 ...spectroscopy and F140W imaging, allowing us to derive secure redshifts down to M sub(140) ~ 25.5 AB and 3sigma line fluxes of ~5 x 10 super(-18) erg s super(-1) cm super(-2). In particular, we were able to spectroscopically confirm 12 early-type galaxies (ETGs) in the field up to z ~ 3, 6 of which are in the cluster core, which represents the first direct spectroscopic confirmation of quiescent galaxies in a z = 2 cluster environment. With 140 redshifts in a ~6 arcmin super(2) field, we can trace the spatial and redshift galaxy distribution in the cluster core and background field. We find two strong peaks at z = 2.00 and z = 2.07, where only one was seen in our previously published ground-based data. Due to the spectroscopic confirmation of the cluster ETGs, we can now reevaluate the redshift of Cl J1449+0856 at z = 2.00, rather than z = 2.07, with the background overdensity being revealed to be sparse and "sheet"-like. This presents an interesting case of chance alignment of two close yet unrelated structures, each one preferentially selected by different observing strategies. With 6 quiescent or early-type spectroscopic members and 20 star-forming ones, Cl J1449+0856 is now reliably confirmed to be at z = 2.00. The identified members can now allow for a detailed study of galaxy properties in the densest environment at z = 2.
We have discovered a 300 kpc-wide giant Lyman-
α
(Ly
α
) nebula centered on the massive galaxy group RO-1001 at
z
= 2.91 in the Cosmic Evolution Survey field. Keck Cosmic Web Imager observations ...reveal three cold gas filaments converging into the center of the potential well of its ∼4 × 10
13
M
⊙
dark matter halo, hosting 1200
M
⊙
yr
−1
of star formation as probed by Atacama Large Millimeter Array and NOrthern Extended Millimeter Array observations. The nebula morphological and kinematics properties and the prevalence of blueshifted components in the Ly
α
spectra are consistent with a scenario of gas accretion. The upper limits on active galactic nuclei activity and overall energetics favor gravity as the primary Ly
α
powering source and infall as the main source of gas flows to the system. Although interpretational difficulties remain, with outflows and likely also photoionization with ensuing recombination still playing a role, this finding provides arguably an ideal environment to quantitatively test models of cold gas accretion and galaxy feeding inside an actively star-forming massive halo at high redshift.
We use deep panchromatic data sets in the GOODS-N field, from GALEX to the deepest Herschel far-infrared (FIR) and VLA radio continuum imaging, to explore the evolution of star-formation activity and ...dust attenuation properties of star-forming galaxies to z Asymptotically = to 4, using mass-complete samples. Our main results can be summarized as follows: (i) the slope of the star-formation rate-M sub(*) correlation is consistent with being constant Asymptotically = to0.8 up to z Asymptotically = to 1.5, while its normalization keeps increasing with redshift; (ii) for the first time we are able to explore the FIR-radio correlation for a mass-selected sample of star-forming galaxies: the correlation does not evolve up to z Asymptotically = to 4; (iii) we confirm that galaxy stellar mass is a robust proxy for UV dust attenuation in star-forming galaxies, with more massive galaxies being more dust attenuated. Strikingly, we find that this attenuation relation evolves very weakly with redshift, with the amount of dust attenuation increasing by less than 0.3 mag over the redshift range 0.5-4 for a fixed stellar mass; (iv) the correlation between dust attenuation and the UV spectral slope evolves with redshift, with the median UV slope becoming bluer with redshift. By z Asymptotically = to 3, typical UV slopes are inconsistent, given the measured dust attenuations, with the predictions of commonly used empirical laws. (v) Finally, building on existing results, we show that gas reddening is marginally larger (by a factor of around 1.3) than the stellar reddening at all redshifts probed. Our results support a scenario where the ISM conditions of typical star-forming galaxies evolve with redshift, such that at z > or =, slanted 1.5 Main Sequence galaxies have ISM conditions moving closer to those of local starbursts.
We present Atacama Large Millimeter/submillimeter Array observations of the 870 m continuum and CO(4-3) line emission in the core of the galaxy cluster Cl J1449+0856 at z = 2, a near-IR-selected, ...X-ray-detected system in the mass range of typical progenitors of today's massive clusters. The 870 m map reveals six F870 m > 0.5 mJy sources spread over an area of 0.07 arcmin2, giving an overdensity of a factor of ∼10 (6) with respect to blank-field counts down to F870 m > 1 mJy (>0.5 mJy). On the other hand, deep CO(4-3) follow-up confirms membership of three of these sources but suggests that the remaining three, including the brightest 870 m sources in the field (F870 m 2 mJy), are likely interlopers. The measurement of 870 m continuum and CO(4-3) line fluxes at the positions of previously known cluster members provides a deep probe of dusty star formation occurring in the core of this high-redshift structure, adding up to a total star formation rate of ∼700 100 M yr−1 and yielding an integrated star formation rate density of ∼104 M yr−1 Mpc−3, five orders of magnitude larger than in the field at the same epoch, due to the concentration of star-forming galaxies in the small volume of the dense cluster core. The combination of these observations with previously available Hubble Space Telescope imaging highlights the presence in this same volume of a population of galaxies with already suppressed star formation. This diverse composition of galaxy populations in Cl J1449+0856 is especially highlighted at the very cluster center, where a complex assembly of quiescent and star-forming sources is likely forming the future brightest cluster galaxy.
We use Atacama Large Millimetre Array and Jansky Very Large Array observations of the galaxy cluster Cl J1449+0856 at z = 1.99, in order to study how dust-obscured star formation, interstellar medium ...content, and active galactic nuclei activity are linked to environment and galaxy interactions during the crucial phase of high-z cluster assembly, We present detections of multiple transitions of (CO)-C-12, as well as dust continuum emission detections from 11. galaxies in the core of Cl J1449+0856: We measure the gas excitation properties, star formation rates, gas consumption timescales, and gas-to-stellar mass ratios for the galaxies. We find evidence for a large fraction of galaxies with highly excited molecular gas, contributing >50 per cent to the total star formation rate (SFR) in the cluster core. We compare these results with expectations for field galaxies, and conclude that environmental influences have strongly enhanced the fraction of excited galaxies in this cluster. We find a dearth of molecular gas in the galaxies' gas reservoirs, implying a high star formation efficiency (SEE) in the cluster core, and find short gas depletion timescales tau(dep) < 0.1-0.4 Gyr for all galaxies. Interestingly, we do not see evidence for increased specific SFRs (sSFRs) in the cluster galaxies, despite their high SFEs and gas excitations. We rind evidence for a large number of mergers in the cluster core, contributing a large fraction of the core's total star formation compared with expectations in the field. We conclude that the environmental impact on the galaxy excitations is linked to the high rate of galaxy mergers, interactions, and active galactic nuclei in the cluster core
We investigate the stellar population properties of a sample of 24 massive quenched galaxies at 1.25 < z sub(spec) < 2.09 identified in the COSMOS field with our Subaru/Multi-object Infrared Camera ...and Spectrograph near-IR spectroscopic observations. Tracing the stellar population properties as close to their major formation epoch as possible, we try to put constraints on the star formation history, post-quenching evolution, and possible progenitor star-forming populations for such massive quenched galaxies. By using a set of Lick absorption line indices on a rest-frame optical composite spectrum, the average age, metallicity Z/H, and alpha -to-iron element abundance ratio alpha /Fe are derived as log(age/Gyr) = 0.04 super(+0.10) sub(-0.08), Z/H = 0.24 super(+0.20) sub(-0.14), and alpha /Fe = 0.31 super(+0.12) sub(-0.12), respectively. If our sample of quenched galaxies at left angle bracketzright angle bracket = 1.6 is evolved passively to z = 0, their stellar population properties will align in excellent agreement with local counterparts at similar stellar velocity dispersions, which qualifies them as progenitors of local massive early-type galaxies. Redshift evolution of stellar population ages in quenched galaxies combined with low redshift measurements from the literature suggests a formation redshift of z sub(f) ~ 2.3, around which the bulk of stars in these galaxies have been formed. The measured alpha /Fe value indicates a star formation timescale of <, ~1 Gyr, which can be translated into a specific star formation rate of Asymptotically = to1 Gyr super(-1) prior to quenching. Based on these findings, we discuss identifying possible progenitor star-forming galaxies at z Asymptotically = to 2.3. We identify normal star-forming galaxies, i.e., those on the star-forming main sequence, followed by a rapid quenching event, as likely precursors of the quenched galaxies at left angle bracketzright angle bracket = 1.6 presented here.
We study the stellar, brightest cluster galaxy (BCG) and intracluster medium (ICM) masses of 14 South Pole Telescope (SPT) selected galaxy clusters with median redshift z = 0.9 and mass M
...500 = 6 × 1014 M⊙. We estimate stellar masses for each cluster and BCG using six photometric bands, the ICM mass using X-ray observations and the virial masses using the SPT Sunyaev–Zel'dovich effect signature. At z = 0.9, the BCG mass
$M_{\star }^{\mathrm{BCG}}$
constitutes 0.12 ± 0.01 per cent of the halo mass for a 6 × 1014 M⊙ cluster, and this fraction falls as
$M_{500}^{-0.58\pm 0.07}$
. The cluster stellar mass function has a characteristic mass M
0 = 1011.0 ± 0.1 M⊙, and the number of galaxies per unit mass in clusters is larger than in the field by a factor of 1.65 ± 0.20. We combine our SPT sample with previously published samples at low redshift and correct to a common initial mass function and for systematic virial mass differences. We then explore mass and redshift trends in the stellar fraction f
⋆, the ICM fraction f
ICM, the collapsed baryon fraction f
c and the baryon fraction f
b. At a pivot mass of 6 × 1014 M⊙ and redshift z = 0.9, the characteristic values are f
⋆ = 1.1 ± 0.1 per cent, f
ICM = 9.6 ± 0.5 per cent, f
c = 10.7 ± 1.1 per cent and f
b = 10.7 ± 0.6 per cent. These fractions all vary with cluster mass at high significance, with higher mass clusters having lower f
⋆ and f
c and higher f
ICM and f
b. When accounting for a 15 per cent systematic virial mass uncertainty, there is no statistically significant redshift trend at fixed mass. Our results support the scenario where clusters grow through accretion from subclusters (higher f
⋆, lower f
ICM) and the field (lower f
⋆, higher f
ICM), balancing to keep f
⋆ and f
ICM approximately constant since z ∼ 0.9.
ABSTRACT We use Hubble Space Telescope/WFC3 imaging to study the red population in the IR-selected, X-ray detected, low-mass cluster Cl J1449+0856 at z = 2, one of the few bona fide established ...clusters discovered at this redshift, and likely a typical progenitor of an average massive cluster today. This study explores the presence and significance of an early red sequence in the core of this structure, investigating the nature of red-sequence galaxies, highlighting environmental effects on cluster galaxy populations at high redshift, and at the same time underlining similarities and differences with other distant dense environments. Our results suggest that the red population in the core of Cl J1449+0856 is made of a mixture of quiescent and dusty star-forming galaxies, with a seedling of the future red sequence already growing in the very central cluster region, and already characterizing the inner cluster core with respect to lower-density environments. On the other hand, the color-magnitude diagram of this cluster is definitely different from that of lower-redshift z 1 clusters, as well as of some rare particularly evolved massive clusters at similar redshift, and it is suggestive of a transition phase between active star formation and passive evolution occurring in the protocluster and established lower-redshift cluster regimes.
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