Abstract The observed rest-UV luminosity function at cosmic dawn ( z ∼ 8–14) measured by JWST revealed an excess of UV-luminous galaxies relative to many prelaunch theoretical predictions. A high ...star formation efficiency (SFE) and a top-heavy initial mass function (IMF) are among the mechanisms proposed for explaining this excess. Although a top-heavy IMF has been proposed for its ability to increase the light-to-mass ratio (Ψ UV ), the resulting enhanced radiative pressure from young stars could decrease the SFE, potentially driving galaxy luminosities back down. In this Letter, we use idealized radiation hydrodynamic simulations of star cluster formation to explore the effects of a top-heavy IMF on the SFE of clouds typical of the high-pressure conditions found at these redshifts. We find that the SFE in star clusters with solar-neighborhood-like dust abundance decreases with increasingly top-heavy IMFs—by ∼20% for an increase of a factor of 4 in Ψ UV and by 50% for a factor of ∼10 in Ψ UV . However, we find that an expected decrease in the dust-to-gas ratio (∼0.01 × solar) at these redshifts can completely compensate for the enhanced light output. This leads to a (cloud-scale; ∼10 pc) SFE that is ≳70% even for a factor of 10 increase in Ψ UV , implying that highly efficient star formation is unavoidable for high surface density and low-metallicity conditions. Our results suggest that a top-heavy IMF, if present, likely coexists with efficient star formation in these galaxies.
We investigate the origin of the relations between stellar mass and optical circular velocity for early-type galaxies (ETGs) and late-type galaxies (LTGs) - the Faber-Jackson (FJ) and Tully-Fisher ...(TF) relations. We combine measurements of dark halo masses (from satellite kinematics and weak lensing), and the distribution of baryons in galaxies (from a new compilation of galaxy scaling relations), with constraints on dark halo structure from cosmological simulations. The principal unknowns are the halo response to galaxy formation and the stellar initial mass function (IMF). The slopes of the TF and FJ relations are naturally reproduced for a wide range of halo response and IMFs. However, models with a universal IMF and universal halo response cannot simultaneously reproduce the zero-points of both the TF and FJ relations. For a model with a universal Chabrier IMF, LTGs require halo expansion, while ETGs require halo contraction. A Salpeter IMF is permitted for high-mass (σ≳ 180 km s−1) ETGs, but is inconsistent for intermediate masses, unless V
circ(R
e)/σe≳ 1.6. If the IMF is universal and close to Chabrier, we speculate that the presence of a major merger may be responsible for the contraction in ETGs while clumpy accreting streams and/or feedback leads to expansion in LTGs. Alternatively, a recently proposed variation in the IMF disfavours halo contraction in both types of galaxies. Finally we show that our models naturally reproduce flat and featureless circular velocity profiles within the optical regions of galaxies without fine-tuning.
Abstract
We present the first comprehensive release of photometric redshifts (photo
-
z
's) from the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (CANDELS) team. We use statistics ...based upon the Quantile–Quantile (
Q
–
Q
) plot to identify biases and signatures of underestimated or overestimated errors in photo
-
z
probability density functions (PDFs) produced by six groups in the collaboration; correcting for these effects makes the resulting PDFs better match the statistical definition of a PDF. After correcting each group’s PDF, we explore three methods of combining the different groups’ PDFs for a given object into a consensus curve. Two of these methods are based on identifying the minimum
f
-divergence curve, i.e., the PDF that is closest in aggregate to the other PDFs in a set (analogous to the median of an array of numbers). We demonstrate that these techniques yield improved results using sets of spectroscopic redshifts independent of those used to optimize PDF modifications. The best photo
-
z
PDFs and point estimates are achieved with the minimum
f
-divergence using the best four PDFs for each object (mFDa4) and the hierarchical Bayesian (HB4) methods, respectively. The HB4 photo
-
z
point estimates produced
σ
NMAD
= 0.0227/0.0189 and ∣Δ
z
/(1 +
z
)∣ > 0.15 outlier fraction = 0.067/0.019 for spectroscopic and 3D Hubble Space Telescope redshifts, respectively. Finally, we describe the structure and provide guidance for the use of the CANDELS photo
-
z
catalogs, which are available at
https://archive.stsci.edu/prepds/candels/
.
Natural downsizing in hierarchical galaxy formation Neistein, Eyal; Van Den Bosch, Frank C.; Dekel, Avishai
Monthly notices of the Royal Astronomical Society,
10/2006, Letnik:
372, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Stellar-population analyses of today's galaxies show ‘downsizing’, where the stars in more massive galaxies tend to have formed earlier and over a shorter time-span. We show that this phenomenon is ...not necessarily ‘antihierarchical’ but rather has its natural roots in the bottom-up clustering process of dark-matter haloes. While the main progenitor does indeed show an opposite effect, the integrated mass in all the progenitors down to a given minimum mass shows a robust downsizing that is qualitatively similar to what has been observed. These results are derived analytically from the standard extended Press–Schechter (EPS) theory, and are confirmed by merger trees based on EPS or drawn from N-body simulations. The downsizing is valid for any minimum mass, as long as it is the same for all haloes at any given time, but the effect is weaker for smaller minimum mass. If efficient star formation is triggered by atomic cooling, then a minimum halo mass arises naturally from the minimum virial temperature for cooling, T≃ 104 K, though for such a small minimum mass the effect is weaker than observed. Baryonic feedback effects, which are expected to stretch the duration of star formation in small galaxies and shut it down in massive haloes at late epochs, are likely to play a subsequent role in shaping up the final downsizing behaviour. Other appearances of downsizing, such as the decline with time of the typical mass of star-forming galaxies, may not be attributed to the gravitational clustering process but rather arise from the gas processes.
In this paper we present a detailed study of the structures and morphologies of a sample of 1188 massive galaxies with M
* ≥ 1010 M between redshifts z = 1 and 3 within the Ultra Deep Survey (UDS) ...region of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) field. Using this sample we determine how galaxy structure and morphology evolve with time, and investigate the nature of galaxy structure at high redshift. We visually classify our sample into discs, ellipticals and peculiar systems and correct for redshift effects on these classifications through simulations. We find significant evolution in the fractions of galaxies at a given visual classification as a function of redshift. The peculiar population is dominant at z > 2 with a substantial spheroid population, and a negligible disc population. We compute the transition redshift, z
trans, where the combined fraction of spheroidal and disc galaxies is equal to that of the peculiar population, as z
trans = 1.86 ± 0.62 for galaxies in our stellar mass range. We find that this transition changes as a function of stellar mass, with Hubble-type galaxies becoming dominant at higher redshifts for higher mass galaxies (z
trans = 2.22 ± 0.82), than for the lower mass galaxies (z
trans = 1.73 ± 0.57). Higher mass galaxies become morphologically settled before their lower mass counterparts, a form of morphological downsizing. We furthermore compare our visual classifications with the Sérsic index, the concentration, asymmetry and clumpiness (CAS) parameters, star formation rate and rest-frame U − B colour. We find links between the colour of a galaxy, its star formation rate and how extended or peculiar it appears. Finally, we discuss the negligible z > 2 disc fraction based on visual morphologies and speculate that this is an effect of forming disc appearing peculiar through processes such as violent disc instabilities or mergers. We conclude that to properly define and measure high-redshift morphology and structure a new and more exact classification scheme is needed.
We study the correlation of galaxy structural properties with their location relative to the SFR-M* correlation, also known as the star formation 'star-forming main sequence' (SFMS), in the Cosmic ...Assembly Near-infrared Deep Extragalactic Legacy Survey and Galaxy and Mass Assembly Survey and in a semi-analytic model (SAM) of galaxy formation. We first study the distribution of median Sersic index, effective radius, star formation rate (SFR) density and stellar mass density in the SFR-M* plane. We then define a redshift-dependent main sequence and examine the medians of these quantities as a function of distance from this main sequence, both above (higher SFRs) and below (lower SFRs). Finally, we examine the distributions of distance from the main sequence in bins of these quantities. We find strong correlations between all of these galaxy structural properties and the distance from the SFMS, such that as we move from galaxies above the SFMS to those below it, we see a nearly monotonic trend towards higher median Sersic index, smaller radius, lower SFR density, and higher stellar density. In the SAM, bulge growth is driven by mergers and disc instabilities, and is accompanied by the growth of a supermassive black hole which can regulate or quench star formation via active galactic nucleus feedback. We find that our model qualitatively reproduces the trends described above, supporting a picture in which black holes and bulges co-evolve, and active galactic nucleus feedback plays a critical role in moving galaxies off of the SFMS.
ABSTRACT We present estimates of intrinsic scatter in the star formation rate (SFR)-stellar mass (M*) correlation in the redshift range and in the mass range M . We utilize photometry in the Hubble ...Ultradeep Field (HUDF12) and Ultraviolet Ultra Deep Field (UVUDF) campaigns and CANDELS/GOODS-S and estimate SFR, M* from broadband spectral energy distributions and the best-available redshifts. The maximum depth of the UDF photometry (F160W 29.9 AB, 5 depth) probes the SFR-M* correlation down to 107M , a factor of 10-100× lower in M* than previous studies, and comparable to dwarf galaxies in the local universe. We find the slope of the SFR-M* relationship to be near unity at all redshifts and the normalization to decrease with cosmic time. We find a moderate increase in intrinsic scatter with cosmic time from 0.2 to 0.4 dex across the epoch of peak cosmic star formation. None of our redshift bins show a statistically significant increase in intrinsic scatter at low mass. However, it remains possible that intrinsic scatter increases at low mass on timescales shorter than ∼100 Myr. Our results are consistent with a picture of gradual and self-similar assembly of galaxies across more than three orders of magnitude in stellar mass from as low as 107M .
Abstract
Visual inspections of the first optical rest-frame images from JWST have indicated a surprisingly high fraction of disk galaxies at high redshifts. Here, we alternatively apply ...self-supervised machine learning to explore the morphological diversity at
z
≥ 3. Our proposed data-driven representation scheme of galaxy morphologies, calibrated on mock images from the TNG50 simulation, is shown to be robust to noise and to correlate well with the physical properties of the simulated galaxies, including their 3D structure. We apply the method simultaneously to F200W and F356W galaxy images of a mass-complete sample (
M
*
/
M
⊙
> 10
9
) at 3 ≤
z
≤ 6 from the first JWST/NIRCam CEERS data release. We find that the simulated and observed galaxies do not exactly populate the same manifold in the representation space from contrastive learning. We also find that half the galaxies classified as disks—either convolutional neural network-based or visually—populate a similar region of the representation space as TNG50 galaxies with low stellar specific angular momentum and nonoblate structure. Although our data-driven study does not allow us to firmly conclude on the true nature of these galaxies, it suggests that the disk fraction at
z
≥ 3 remains uncertain and possibly overestimated by traditional supervised classifications. Deeper imaging and spectroscopic follow-ups as well as comparisons with other simulations will help to unambiguously determine the true nature of these galaxies, and establish more robust constraints on the emergence of disks at very high redshift.
We investigate the origin of the evolution of the population-averaged central stellar mass density ( 1) of quiescent galaxies (QGs) by probing the relation between stellar age and 1 at z ∼ 0. We use ...the Zurich ENvironmental Study (ZENS), which is a survey of galaxy groups with a large fraction of satellite galaxies. QGs shape a narrow locus in the 1-M plane, which we refer to as 1 ridgeline. Colors of (B − I) and (I − J) are used to divide QGs into three age categories: young (<2 Gyr), intermediate (2-4 Gyr), and old (>4 Gyr). At fixed stellar mass, old QGs on the 1 ridgeline have higher 1 than young QGs. This shows that galaxies landing on the 1 ridgeline at later epochs arrive with lower 1, which drives the zeropoint of the ridgeline down with time. We compare the present-day zeropoint of the oldest population at z = 0 with the zeropoint of the quiescent population 4 Gyr back in time, at z = 0.37. These zeropoints are identical, showing that the intrinsic evolution of individual galaxies after they arrive on the 1 ridgeline must be negligible, or must evolve parallel to the ridgeline during this interval. The observed evolution of the global zeropoint of 0.07 dex over the last 4 Gyr is thus largely due to the continuous addition of newly quenched galaxies with lower 1 at later times ("progenitor bias"). While these results refer to the satellite-rich ZENS sample as a whole, our work suggests a similar age- 1 trend for central galaxies.
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