We quantify the evolution of the stellar mass functions (SMFs) of star-forming and quiescent galaxies as a function of morphology from z ∼ 3 to the present. Our sample consists of ∼50 000 galaxies in ...the CANDELS fields (∼880 arcmin2), which we divide into four main morphological types, i.e. pure bulge-dominated systems, pure spiral disc-dominated, intermediate two-component bulge+disc systems and irregular disturbed galaxies. At z ∼ 2, 80 per cent of the stellar mass density of star-forming galaxies is in irregular systems. However, by z ∼ 0.5, irregular objects only dominate at stellar masses below 109 M⊙. A majority of the star-forming irregulars present at z ∼ 2 undergo a gradual transformation from disturbed to normal spiral disc morphologies by z ∼ 1 without significant interruption to their star formation. Rejuvenation after a quenching event does not seem to be common except perhaps for the most massive objects, because the fraction of bulge-dominated star-forming galaxies with M
*/M⊙ > 1010.7 reaches 40 per cent at z < 1. Quenching implies the presence of a bulge: the abundance of massive red discs is negligible at all redshifts over 2 dex in stellar mass. However, the dominant quenching mechanism evolves. At z > 2, the SMF of quiescent galaxies above M* is dominated by compact spheroids. Quenching at this early epoch destroys the disc and produces a compact remnant unless the star-forming progenitors at even higher redshifts are significantly more dense. At 1 < z < 2, the majority of newly quenched galaxies are discs with a significant central bulge. This suggests that mass quenching at this epoch starts from the inner parts and preserves the disc. At z < 1, the high-mass end of the passive SMF is globally in place and the evolution mostly happens at stellar masses below 1010 M⊙. These low-mass galaxies are compact, bulge-dominated systems, which were environmentally quenched: destruction of the disc through ram-pressure stripping is the likely process.
We measure new estimates for the galaxy stellar mass function and star formation rates for samples of galaxies at z ∼ 4, 5, 6 and 7 using data in the CANDELS GOODS South field. The deep near-infrared ...observations allow us to construct the stellar mass function at z ≥ 6 directly for the first time. We estimate stellar masses for our sample by fitting the observed spectral energy distributions with synthetic stellar populations, including nebular line and continuum emission. The observed UV luminosity functions for the samples are consistent with previous observations; however, we find that the observed M
UV-M
* relation has a shallow slope more consistent with a constant mass-to-light ratio and a normalization which evolves with redshift. Our stellar mass functions have steep low-mass slopes (α ≈ −1.9), steeper than previously observed at these redshifts and closer to that of the UV luminosity function. Integrating our new mass functions, we find the observed stellar mass density evolves from
$\log _{10} \rho _{*} = 6.64^{+0.58}_{-0.89}$
at z ∼ 7 to 7.36 ± 0.06 M⊙ Mpc− 3 at z ∼ 4. Finally, combining the measured UV continuum slopes (β) with their rest-frame UV luminosities, we calculate dust-corrected star formation rates (SFR) for our sample. We find the specific SFR for a fixed stellar mass increases with redshift whilst the global SFR density falls rapidly over this period. Our new SFR density estimates are higher than previously observed at this redshift.
The analysis of galaxies on the star formation rate-stellar mass (SFR–M∗) plane is a powerful diagnostic for galaxy evolution at different cosmic times. We consider a sample of 24 463 galaxies from ...the CANDELS/GOODS-S survey to conduct a detailed analysis of the SFR–M∗ relation at redshifts \hbox{$0.5\leqslant z<$}0.5 ⩽ z<3 over more than three dex in stellar mass. To obtain SFR estimates, we utilise mid- and far-IR photometry when available, and rest-UV fluxes for all the other galaxies. We perform our analysis in different redshift bins, with two different methods: 1) a linear regression fitting of all star-forming galaxies, defined as those with specific SFRs log 10(sSFR/ yr-1) > −9.8, similarly to what is typically done in the literature; 2) a multi-Gaussian decomposition to identify the galaxy main sequence (MS), the starburst sequence and the quenched galaxy cloud. We find that the MS slope becomes flatter when higher stellar mass cuts are adopted, and that the apparent slope change observed at high masses depends on the SFR estimation method. In addition, the multi-Gaussian decomposition reveals the presence of a starburst population which increases towards low stellar masses and high redshifts. We find that starbursts make up ~ 5% of all galaxies at z = 0.5−1.0, while they account for ~ 16% of galaxies at 2 <z< 3 with log10(M∗/M0) = 8.25–11.25. We conclude that the dissection of the SFR–M∗ in multiple components over a wide range of stellar masses is necessary to understand the importance of the different modes of star formation through cosmic time.
Of several dozen galaxies observed spectroscopically that are candidates for having a redshift (z) in excess of seven, only five have had their redshifts confirmed via Lyman α emission, at z = 7.008, ...7.045, 7.109, 7.213 and 7.215 (refs 1-4). The small fraction of confirmed galaxies may indicate that the neutral fraction in the intergalactic medium rises quickly at z > 6.5, given that Lyman α is resonantly scattered by neutral gas. The small samples and limited depth of previous observations, however, makes these conclusions tentative. Here we report a deep near-infrared spectroscopic survey of 43 photometrically-selected galaxies with z > 6.5. We detect a near-infrared emission line from only a single galaxy, confirming that some process is making Lyman α difficult to detect. The detected emission line at a wavelength of 1.0343 micrometres is likely to be Lyman α emission, placing this galaxy at a redshift z = 7.51, an epoch 700 million years after the Big Bang. This galaxy's colours are consistent with significant metal content, implying that galaxies become enriched rapidly. We calculate a surprisingly high star-formation rate of about 330 solar masses per year, which is more than a factor of 100 greater than that seen in the Milky Way. Such a galaxy is unexpected in a survey of our size, suggesting that the early Universe may harbour a larger number of intense sites of star formation than expected.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
While major mergers have long been proposed as a driver of both active galactic nucleus (AGN) activity and the relation, studies of moderate to high-redshift Seyfert-luminosity AGN hosts have found ...little evidence for enhanced rates of interactions. However, both theory and observation suggest that while these AGNs may be fueled by stochastic accretion and secular processes, high-luminosity, high-redshift, and heavily obscured AGNs are the AGNs most likely to be merger-driven. To better sample this population of AGNs, we turn to infrared selection in the CANDELS/COSMOS field. Compared to their lower-luminosity and less obscured X-ray-only counterparts, IR-only AGNs (luminous, heavily obscured AGNs) are more likely to be classified as either irregular ( versus ) or asymmetric ( versus ) and are less likely to have a spheroidal component ( versus ). Furthermore, IR-only AGNs are also significantly more likely than X-ray-only AGNs ( versus ) to be classified either as interacting or merging in a way that significantly disturbs the host galaxy or as disturbed, though not clearly interacting or merging, which potentially represents the late stages of a major merger. This suggests that while major mergers may not contribute significantly to the fueling of Seyfert-luminosity AGNs, interactions appear to play a more dominant role in the triggering and fueling of high-luminosity heavily obscured AGNs.
We present the results of a study investigating the sizes and morphologies of redshift 4 < z < 8 galaxies in the CANDELS (Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey) GOODS-S ...(Great Observatories Origins Deep Survey southern field), HUDF (Hubble Ultra-Deep Field) and HUDF parallel fields. Based on non-parametric measurements and incorporating a careful treatment of measurement biases, we quantify the typical size of galaxies at each redshift as the peak of the lognormal size distribution, rather than the arithmetic mean size. Parametrizing the evolution of galaxy half-light radius as r
50 ∝ (1 + z)
n
, we find n = −0.20 ± 0.26 at bright UV-luminosities (0.3L
*(z = 3) < L < L
*) and n = −0.47 ± 0.62 at faint luminosities (0.12L
* < L < 0.3L
*). Furthermore, simulations based on artificially redshifting our z ∼ 4 galaxy sample show that we cannot reject the null hypothesis of no size evolution. We show that this result is caused by a combination of the size-dependent completeness of high-redshift galaxy samples and the underestimation of the sizes of the largest galaxies at a given epoch. To explore the evolution of galaxy morphology we first compare asymmetry measurements to those from a large sample of simulated single Sérsic profiles, in order to robustly categorize galaxies as either ‘smooth’ or ‘disturbed’. Comparing the disturbed fraction amongst bright (M
1500 ≤ −20) galaxies at each redshift to that obtained by artificially redshifting our z ∼ 4 galaxy sample, while carefully matching the size and UV-luminosity distributions, we find no clear evidence for evolution in galaxy morphology over the redshift interval 4 < z < 8. Therefore, based on our results, a bright (M
1500 ≤ −20) galaxy at z ∼ 6 is no more likely to be measured as ‘disturbed’ than a comparable galaxy at z ∼ 4, given the current observational constraints.
What are the faintest distant galaxies we can see with the Hubble Space Telescope (HST) now, before the launch of the James Webb Space Telescope? This is the challenge taken up by the Frontier ...Fields, a Director's discretionary time campaign with HST and the Spitzer Space Telescope to see deeper into the universe than ever before. The Frontier Fields combines the power of HST and Spitzer with the natural gravitational telescopes of massive high-magnification clusters of galaxies to produce the deepest observations of clusters and their lensed galaxies ever obtained. Six clusters-Abell 2744, MACSJ0416.1-2403, MACSJ0717.5+3745, MACSJ1149.5+2223, Abell S1063, and Abell 370-have been targeted by the HST ACS/WFC and WFC3/IR cameras with coordinated parallel fields for over 840 HST orbits. The parallel fields are the second-deepest observations thus far by HST with 5 point-source depths of ∼29th ABmag. Galaxies behind the clusters experience typical magnification factors of a few, with small regions magnified by factors of 10-100. Therefore, the Frontier Field cluster HST images achieve intrinsic depths of ∼30-33 mag over very small volumes. Spitzer has obtained over 1000 hr of Director's discretionary imaging of the Frontier Field cluster and parallels in IRAC 3.6 and 4.5 m bands to 5 point-source depths of ∼26.5, 26.0 ABmag. We demonstrate the exceptional sensitivity of the HST Frontier Field images to faint high-redshift galaxies, and review the initial results related to the primary science goals.
ABSTRACT The Spitzer-Cosmic Assembly Deep Near-infrared Extragalactic Legacy Survey (S-CANDELS; PI G.Fazio) is a Cycle 8 Exploration Program designed to detect galaxies at very high redshifts ( ). To ...mitigate the effects of cosmic variance and also to take advantage of deep coextensive coverage in multiple bands by the Hubble Space Telescope (HST) Multi-cycle Treasury Program CANDELS, S-CANDELS was carried out within five widely separated extragalactic fields: the UKIDSS Ultra-deep Survey, the Extended Chandra Deep Field South, COSMOS, the HST Deep Field North, and the Extended Groth Strip. S-CANDELS builds upon the existing coverage of these fields from the Spitzer Extended Deep Survey (SEDS), a Cycle 6 Exploration Program, by increasing the integration time from SEDS' 12 hr to a total of 50 hr but within a smaller area, 0.16 deg2. The additional depth significantly increases the survey completeness at faint magnitudes. This paper describes the S-CANDELS survey design, processing, and publicly available data products. We present Infrared Array Camera (IRAC) dual-band catalogs reaching to a depth of 26.5 AB mag. Deep IRAC counts for the roughly 135,000 galaxies detected by S-CANDELS are consistent with models based on known galaxy populations. The increase in depth beyond earlier Spitzer/IRAC surveys does not reveal a significant additional contribution from discrete sources to the diffuse Cosmic Infrared Background (CIB). Thus it remains true that only roughly half of the estimated CIB flux from COBE/DIRBE is resolved.
We have used high-resolution, Hubble Space Telescope, near-infrared imaging to conduct a detailed analysis of the morphological properties of the most massive galaxies at high redshift, modelling the ...WFC3/IR H
160-band images of the ≃200 galaxies in the CANDELS-UDS field with photometric redshifts 1 < z < 3, and stellar masses M
* > 1011 M⊙. We have explored the results of fitting single-Sérsic and bulge+disc models, and have investigated the additional errors and potential biases introduced by uncertainties in the background and the on-image point spread function. This approach has enabled us to obtain formally acceptable model fits to the WFC3/IR images of >90 per cent of the galaxies. Our results indicate that these massive galaxies at 1 < z < 3 lie both on and below the local size-mass relation, with a median effective radius of ∼2.6 kpc, a factor of ≃2.3 smaller than comparably massive local galaxies. Moreover, we find that bulge-dominated objects in particular show evidence for a growing bimodality in the size-mass relation with increasing redshift, and by z > 2 the compact bulges display effective radii a factor of ≃4 smaller than local ellipticals of comparable mass. These trends also appear to extend to the bulge components of disc-dominated galaxies. In addition, we find that, while such massive galaxies at low redshift are generally bulge-dominated, at redshifts 1 < z < 2 they are predominantly mixed bulge+disc systems, and by z > 2 they are mostly disc-dominated. The majority of the disc-dominated galaxies are actively forming stars, although this is also true for many of the bulge-dominated systems. Interestingly, however, while most of the quiescent galaxies are bulge-dominated, we find that a significant fraction (25-40 per cent) of the most quiescent galaxies, with specific star formation rates sSFR < 10−10 yr−1, have disc-dominated morphologies. Thus, while our results show that the massive galaxy population is undergoing dramatic changes at this crucial epoch, they also suggest that the physical mechanisms which quench star formation activity are not simply connected to those responsible for the morphological transformation of massive galaxies into present-day giant ellipticals.
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