The peak star formation intensity in starburst galaxies does not vary significantly from the local universe to redshift z similar to 6. We arrive at this conclusion through new surface brightness ...measurements of 47 starburst galaxies at z unk 5-6, doubling the redshift range for such observations. These galaxies are spectroscoplcally confirmed in the Hubble Ultra Deep Field (HUDF) through the GRism ACS program for Extragalactic Science (GRAPES) project. The starburst intensity limit for galaxies at z unk 5-6 agrees with those at z unk 3 4 and z unk 6 to within a factor of a few, after correcting for cosmological surface brightness dimming and for dust. The most natural interpretation of this constancy over cosmic time is that the same physical mechanisms limit starburst intensity at all redshifts up to z unk 6 (be they galactic winds, gravitational instability, or something else). We do see two trends with redshift: First, the UV spectral slope ( beta ) of galaxies at z unk 5-6 is bluer than that of z unk 3 galaxies, suggesting an increase in dust content over time. Second, the galaxy sizes from z unk 3 to 6 scale approximately as the Hubble parameter H super(-1) (z unk. Thus, galaxies at z unk 6 are high-redshift starbursts, much like their local analogs except for slightly bluer colors, smaller physical sizes, and correspondingly lower overall luminosities. If we now assume a constant maximum star formation intensity, the differences in observed surface brightness between z unk 6 and 6 are consistent with standard expanding cosmology and strongly inconsistent with the tired light model.
The properties of stellar clumps in star-forming galaxies and their evolution over the redshift range 2 ≲ z ≲ 6 are presented and discussed in the context of the build-up of massive galaxies at early ...cosmic times. We focused on galaxies with spectroscopic redshifts from the VIMOS Ultra Deep Survey (VUDS) and stellar masses log 10(M⋆/M⊙) > −0.204 × (z−4.5) + 9.35. We analyzed HST-ACS images to identify clumps within a 20 kpc radius using a method taking into account differential surface brightness dimming and luminosity evolution with redshift. We find that the population of galaxies with more than one clump is dominated by galaxies with two clumps, representing ~21–25% of the population, while the fraction of galaxies with three, or four and more, clumps is 8–11% and 7–9%, respectively. The fraction of clumpy galaxies is in the range ~35–55% over 2 < z < 6, increasing at higher redshifts, indicating that the fraction of irregular galaxies remains high up to the highest redshifts. The large and bright clumps (M⋆ ~ 109 up to ~1010 M⊙) are found to reside predominantly in galaxies with two clumps. Smaller and lower luminosity clumps (M⋆ < 109 M⊙) are found in galaxies with three clumps or more. We interpret these results as evidence for two different modes of clump formation working in parallel. The small low luminosity clumps are likely the result of disk fragmentation, with violent disk instabilities (VDI) forming several long-lived clumps in-situ as suggested from simulations. A fraction of these clumps is also likely coming from minor mergers as confirmed from spectroscopy in several cases. The clumps in the dominating population of galaxies with two clumps are significantly more massive and have properties akin to those in galaxy pairs undergoing massive merging observed at similar redshifts; they appear as more massive than the most massive clumps observed in numerical simulations of disks with VDI. We infer from these properties that the bright and large clumps are most likely the result of major mergers bringing-in ex situ matter onto a galaxy, and we derive a high major merger fraction of ~20%. The diversity of clump properties therefore suggests that the assembly of star-forming galaxies at z ~ 2–6 proceeds from several different dissipative processes including an important contribution from major and minor mergers.
Aims.
Our aim is to analyze the variance of the intergalactic medium (IGM) transmission by studying this parameter in the rest-frame UV spectra of a large sample of high-redshift galaxies.
Methods.
...We made use of the VIMOS Ultra Deep Survey and the VANDELS public survey to gain insight into the far UV spectrum of 2.7 <
z
< 6 galaxies. Using the SPARTAN fitting software, we estimated the IGM toward individual galaxies and then divided them into two sub-samples characterized by a transmission above or below the theoretical prescription. We created average spectra of combined VUDS and VANDELS data for each set of galaxies in seven redshift bins.
Results.
The resulting spectra clearly exhibit the variance of the IGM transmission that can be seen directly from high-redshift galaxy observations. Computing the optical depth based on the IGM transmission, we find an excellent agreement with results for quasi-stellar objects. In addition, our measurements appear to suggest that there is a large dispersion of redshift where a complete Gunn-Peterson Trough occurs, depending on the line of sight.
The Epoch of Reionization (EoR) began when galaxies grew in abundance and luminosity, so their escaping Lyman continuum (LyC) radiation started ionizing the surrounding neutral intergalactic medium ...(IGM). Despite significant recent progress, the nature and role of cosmic reionizers are still unclear: in order to define them, it would be necessary to directly measure their LyC escape fraction ( f esc ). However, this is impossible during the EoR due to the opacity of the IGM. Consequently, many efforts at low and intermediate redshift have been made to determine measurable indirect indicators in high-redshift galaxies so that their f esc can be predicted. This work presents the analysis of the indirect indicators of 62 spectroscopically confirmed star-forming galaxies at 6 ≤ z ≤ 9 from the Cosmic Evolution Early Release Science (CEERS) survey, combined with 12 sources with public data from other JWST-ERS campaigns. From the NIRCam and NIRSpec observations, we measured their physical and spectroscopic properties. We discovered that on average 6 < z < 9 star-forming galaxies are compact in the rest-frame UV ( r e ∼ 0.4 kpc), are blue sources (UV- β slope ∼ − 2.17), and have a predicted f esc of about 0.13. A comparison of our results to models and predictions as well as an estimation of the ionizing budget suggests that low-mass galaxies with UV magnitudes fainter than M 1500 = −18 that we currently do not characterize with JWST observations probably played a key role in the process of reionization.
ABSTRACT
We study the projected spatial offset between the ultraviolet continuum and Ly α emission for 65 lensed and unlensed galaxies in the Epoch of Reionization (5 ≤ z ≤ 7), the first such study ...at these redshifts, in order to understand the potential for these offsets to confuse estimates of the Ly α properties of galaxies observed in slit spectroscopy. While we find that ∼40 per cent of galaxies in our sample show significant projected spatial offsets ($|\Delta _{\rm {Ly}\alpha -\rm {UV}}|$), we find a relatively modest average projected offset of $|\widetilde{\Delta }_{\rm {Ly}\alpha -\rm {UV}}|$ = 0.61 ± 0.08 proper kpc for the entire sample. A small fraction of our sample, ∼10 per cent, exhibit offsets in excess of 2 proper kpc, with offsets seen up to ∼4 proper kpc, sizes that are considerably larger than the effective radii of typical galaxies at these redshifts. An internal comparison and a comparison to studies at lower redshift yielded no significant evidence of evolution of $|\Delta _{\rm {Ly}\alpha -\rm {UV}}|$ with redshift. In our sample, ultraviolet (UV)-bright galaxies ($\widetilde{L_{\mathrm{ UV}}}/L^{\ast }_{\mathrm{ UV}}=0.67$) showed offsets a factor of three greater than their fainter counterparts ($\widetilde{L_{\mathrm{ UV}}}/L^{\ast }_{\mathrm{ UV}}=0.10$), 0.89 ± 0.18 versus 0.27 ± 0.05 proper kpc, respectively. The presence of companion galaxies and early stage merging activity appeared to be unlikely causes of these offsets. Rather, these offsets appear consistent with a scenario in which internal anisotropic processes resulting from stellar feedback, which is stronger in UV-brighter galaxies, facilitate Ly α fluorescence and/or backscattering from nearby or outflowing gas. The reduction in the Ly α flux due to offsets was quantified. It was found that the differential loss of Ly α photons for galaxies with average offsets is not, if corrected for, a limiting factor for all but the narrowest slit widths (<0.4 arcsec). However, for the largest offsets, if they are mostly perpendicular to the slit major axis, slit losses were found to be extremely severe in cases where slit widths of ≤1 arcsec were employed, such as those planned for James Webb Space Telescope/NIRSpec observations.
We report on a Hubble Space Telescope search for rest-frame ultraviolet emission from the host galaxies of five far-infrared-luminous z 6 quasars and the z = 5.85 hot-dust-free quasar SDSS ...J0005-0006. We perform 2D surface brightness modeling for each quasar using a Markov Chain Monte Carlo estimator, to simultaneously fit and subtract the quasar point source in order to constrain the underlying host galaxy emission. We measure upper limits for the quasar host galaxies of mJ > 22.7 mag and mH > 22.4 mag, corresponding to stellar masses of M* < 2 × 1011M . These stellar mass limits are consistent with the local MBH − M* relation. Our flux limits are consistent with those predicted for the UV stellar populations of z 6 host galaxies, but likely in the presence of significant dust ( mag). We also detect a total of up to nine potential z 6 quasar companion galaxies surrounding five of the six quasars, separated from the quasars by 1 4-3 2, or 8.4-19.4 kpc, which may be interacting with the quasar hosts. These nearby companion galaxies have UV absolute magnitudes of −22.1 to −19.9 mag and UV spectral slopes β of −2.0 to −0.2, consistent with luminous star-forming galaxies at z 6. These results suggest that the quasars are in dense environments typical of luminous z 6 galaxies. However, we cannot rule out the possibility that some of these companions are foreground interlopers. Infrared observations with the James Webb Space Telescope will be needed to detect the z 6 quasar host galaxies and better constrain their stellar mass and dust content.
ABSTRACT
The physical properties of Epoch of Reionization (EoR) galaxies are still poorly constrained by observations. To better understand the ionizing properties of galaxies in the EoR, we ...investigate deep, rest-frame ultraviolet (UV) spectra of ≃500 star-forming galaxies at 3 ≤ z ≤ 5 selected from the public ESO-VANDELS spectroscopic survey. The absolute ionizing photon escape fraction ($f_{\rm esc}^{\rm abs}$, i.e. the ratio of leaking against produced ionizing photons) is derived by combining absorption line measurements with estimates of the UV attenuation. The ionizing production efficiency (ξion, i.e. the number of ionizing photons produced per non-ionizing UV luminosity) is calculated by fitting the far-UV (FUV) stellar continuum of the VANDELS galaxies. We find that the $f_{\rm esc}^{\rm abs}$ and ξion parameters increase towards low-mass, blue UV-continuum slopes and strong Ly α emitting galaxies, and both are slightly higher-than-average for the UV-faintest galaxies in the sample. Potential Lyman Continuum Emitters (LCEs, $f_{\rm esc}^{\rm abs} \ge 5{{\ \rm \, per\ cent}}$) and selected Lyman Alpha Emitters (LAEs, WLyα ≤ −20 Å) show systematically higher ξion (log ξion(Hz erg−1) ≈ 25.38, 25.41) than non-LCEs and non-LAEs (log ξion(Hz erg−1) ≈ 25.18, 25.14) at similar UV magnitudes. This indicates very young underlying stellar populations (≈10 Myr) at relatively low metallicities (≈0.2 Z⊙). The FUV non-ionizing spectra of potential LCEs is characterized by blue UV slopes (≤−2), enhanced Ly α emission (≤−25 Å), strong UV nebular lines (e.g. high ${\rm C\, \small {IV}}$1550/${\rm C\, \small {III}}$1908 ≥0.75 ratios), and weak absorption lines (≤1 Å). The latter suggests the existence of low gas-column-density channels in the interstellar medium, which enables the escape of ionizing photons. By comparing our VANDELS results against other surveys in the literature, our findings imply that the ionizing budget in the EoR was likely dominated by UV-faint, low-mass, and dustless galaxies.
We present the size evolution of passively evolving galaxies at z ~ 2 identified in Wide-Field Camera 3 imaging from the Early Release Science program. Our sample was constructed using an analog to ...the passive BzK galaxy selection criterion, which isolates galaxies with little or no ongoing star formation at z > ~ 1.5. We identify 30 galaxies in ~40 arcmin super(2) to H < 25 mag. By fitting the 10-band Hubble Space Telescope photometry from 0.22 mu m < ~ lambda sub(obs) < ~ 1.6 mu m with stellar population synthesis models, we simultaneously determine photometric redshift, stellar mass, and a bevy of other population parameters. Based on the six galaxies with published spectroscopic redshifts, we estimate a typical redshift uncertainty of ~0.033(1 + z). We determine effective radii from Sersic profile fits to the H-band image using an empirical point-spread function. By supplementing our data with published samples, we propose a mass-dependent size evolution model for passively evolving galaxies, where the most massive galaxies (Mlow * ~ 10 super(11) M) undergo the strongest evolution from z ~ 2 to the present. Parameterizing the size evolution as (1 + z) super(- alpha ), we find a tentative scaling of alpha approx = (- 0.6 + or - 0.7) + (0.9 + or - 0.4)log(Mlow */10 super(9) M sub(middot in circle)), where the relatively large uncertainties reflect the poor sampling in stellar mass due to the low numbers of high-redshift systems. We discuss the implications of this result for the redshift evolution of the Mlow *-R sub(e) relation for red galaxies.
The ALPINE-ALMA [CII] survey Gruppioni, C.; Béthermin, M.; Loiacono, F. ...
Astronomy and astrophysics (Berlin),
11/2020, Letnik:
643
Journal Article
Recenzirano
Odprti dostop
Aims.
We present the detailed characterisation of a sample of 56 sources serendipitously detected in ALMA band 7 as part of the ALMA Large Program to INvestigate CII at Early Times (ALPINE). These ...sources, detected in COSMOS and ECDFS, have been used to derive the total infrared luminosity function (LF) and to estimate the cosmic star formation rate density (SFRD) up to
z
≃ 6.
Methods.
We looked for counterparts of the ALMA sources in all the available multi-wavelength (from HST to VLA) and photometric redshift catalogues. We also made use of deeper UltraVISTA and
Spitzer
source lists and maps to identify optically dark sources with no matches in the public catalogues. We used the sources with estimated redshifts to derive the 250
μ
m rest-frame and total infrared (8–1000
μ
m) LFs from
z
≃ 0.5 to 6.
Results.
Our ALMA blind survey (860
μ
m flux density range: ∼0.3–12.5 mJy) allows us to further push the study of the nature and evolution of dusty galaxies at high-
z
, identifying luminous and massive sources to redshifts and faint luminosities never probed before by any far-infrared surveys. The ALPINE data are the first ones to sample the faint end of the infrared LF, showing little evolution from
z
≃ 2.5 to
z
≃ 6, and a “flat” slope up to the highest redshifts (i.e. 4.5 <
z
< 6). The SFRD obtained by integrating the luminosity function remains almost constant between
z
≃ 2 and
z
≃ 6, and significantly higher than the optical or ultra-violet derivations, showing a significant contribution of dusty galaxies and obscured star formation at high-
z
. About 14% of all the ALPINE serendipitous continuum sources are found to be optically and near-infrared (near-IR) dark (to a depth
K
s
∼ 24.9 mag). Six show a counterpart only in the mid-IR and no HST or near-IR identification, while two are detected as C II emitters at
z
≃ 5. The six HST+near-IR dark galaxies with mid-IR counterparts are found to contribute about 17% of the total SFRD at
z
≃ 5 and to dominate the high-mass end of the stellar mass function at
z
> 3.
Abstract
We present a self-consistent model of the Milky Way to reproduce the observed distributions (spectral type, absolute
J
-band magnitude, effective temperature) and total velocity dispersion ...of brown dwarfs. For our model, we adopt parametric forms for the star formation history and initial-mass function, published evolutionary models, and theoretical age–velocity relations. Using standard Markov Chain Monte Carlo methods, we derive a power-law index of the initial-mass function of
α
= −0.71 ± 0.11, which is an improvement over previous studies. We consider a gamma-function form for the star formation history, though we find that this complex model is only slightly favored over a declining exponential. We find that a velocity variance that linearly increases with age and has an initial value of
σ
0
=
9.0
−
9.0
+
11
km s
−1
best reproduces the total velocity dispersions. Given the similarities to main-sequence stars, this suggests brown dwarfs likely form via similar processes, but we recognize that the sizable uncertainties on
σ
0
preclude firm conclusions. To further refine these conclusions, we suggest that wide-field infrared imaging or low-resolution spectroscopic surveys, such as with the Nancy Grace Roman Space Telescope or Euclid, could provide large samples of brown dwarfs with robust spectral types that could probe the thickness of the thin disk. In this way, the number counts and population demographics could probe the same physical processes as with the kinematic measurements, however may provide larger samples and be subject to different selection biases.
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