We report subarcsecond resolution IRAM PdBI millimeter CO interferometry of four z ~ 2 submillimeter galaxies (SMGs), and sensitive CO(3-2) flux limits toward three z ~ 2 UV/optically selected ...star-forming galaxies. The new data reveal for the first time spatially resolved CO gas kinematics in the observed SMGs. Two of the SMGs show double or multiple morphologies, with complex, disturbed gas motions. The other two SMGs exhibit CO velocity gradients of ~500 km s-1 across <=0.2'' (1.6 kpc) diameter regions, suggesting that the star-forming gas is in compact, rotating disks. Our data provide compelling evidence that these SMGs represent extreme, short-lived "maximum" star-forming events in highly dissipative mergers of gas-rich galaxies. The resulting high-mass surface and volume densities of SMGs are similar to those of compact quiescent galaxies in the same redshift range and much higher than those in local spheroids. From the ratio of the comoving volume densities of SMGs and quiescent galaxies in the same mass and redshift ranges, and from the comparison of gas exhaustion timescales and stellar ages, we estimate that the SMG phase duration is about 100 Myr. Our analysis of SMGs and optically/UV selected high-redshift star-forming galaxies supports a "universal" Chabrier IMF as being valid over the star-forming history of these galaxies. We find that the 12CO luminosity to total gas mass conversion factors at z ~ 2-3 are probably similar to those assumed at z ~ 0. The implied gas fractions in our sample galaxies range from 20% to 50%. Based on observations obtained at the IRAM Plateau de Bure Interferometer (PdBI). IRAM is funded by the Centre National de la Recherché Scientifique (France), the Max-Planck Gesellschaft (Germany), and the Instituto Geografico Nacional (Spain).
We present the analysis of Hubble Space Telescope (HST) J- and H-band imaging for 29 galaxies on the star-forming main sequence at z ~ 2, which have adaptive optics Very Large Telescope SINFONI ...integral field spectroscopy from our SINS/zC-SINF program. The SINFONI H alpha data resolve the ongoing star formation and the ionized gas kinematics on scales of 1-2 kpc; the near-IR images trace the galaxies' rest-frame optical morphologies and distributions of stellar mass in old stellar populations at a similar resolution. The global light profiles of most galaxies show disk-like properties well described by a single Sersic profile with n ~ 1, with only ~ 15% requiring a high n > 3 Sersic index, all more massive than 10 super(10) M sub(middot in circle). This is attributed to differences in sample selection and definitions of size and/or mass measurements.
We present deep and high-resolution Hubble Space Telescope NIC2 F160W imaging at 1.6 Delta *mm of six z ~ 2 star-forming galaxies with existing near-infrared integral field spectroscopy from SINFONI ...at the Very Large Telescope. The unique combination of rest-frame optical imaging and nebular emission-line maps provides simultaneous insight into morphologies and dynamical properties. The overall rest-frame optical emission of the galaxies is characterized by shallow profiles in general (Sersic index n < 1), with median effective radii of R e ~ 5 kpc. The morphologies are significantly clumpy and irregular, which we quantify through a non-parametric morphological approach, estimating the Gini (G), multiplicity ( Delta *V), and M 20 coefficients. The estimated strength of the rest-frame optical emission lines in the F160W bandpass indicates that the observed structure is not dominated by the morphology of line-emitting gas, and must reflect the underlying stellar mass distribution of the galaxies. The sizes and structural parameters in the rest-frame optical continuum and H Delta *a emission reveal no significant differences, suggesting similar global distributions of the ongoing star formation and more evolved stellar population. While no strong correlations are observed between stellar population parameters and morphology within the NIC2/SINFONI sample itself, a consideration of the sample in the context of a broader range of z ~ 2 galaxy types (K-selected quiescent, active galactic nucleus, and star forming; 24 Delta *mm selected dusty, infrared-luminous) indicates that these galaxies probe the high specific star formation rate and low stellar mass surface density part of the massive z ~ 2 galaxy population, with correspondingly large effective radii, low Sersic indices, low G, and high Delta *V and M 20. The combined NIC2 and SINFONI data set yields insights of unprecedented detail into the nature of mass accretion at high redshift.
ABSTRACT
We present a study of the connection between the escape fraction of Lyman-alpha ($\mathrm{Ly\, \alpha }$) and Lyman-continuum (LyC) photons within a sample of N = 152 star-forming galaxies ...selected from the VANDELS survey at 3.85 ≤ zspec ≤ 4.95 (〈zspec〉 = 4.36). By combining measurements of H$\, \alpha$ equivalent width $(W_{\rm {\lambda }}(\rm {H\, \alpha }))$ derived from broad-band photometry with measurements of Ly$\, \alpha$ equivalent width $(W_{\rm {\lambda }}(\rm {Ly\, \alpha }))$ from the VANDELS spectra, we individually estimate $f_{\rm {esc}}^{\rm {Ly\alpha }}$ for our full sample. In agreement with previous studies, we find a positive correlation between $W_{\rm {\lambda }}(\rm {Ly\, \alpha })$ and $f_{\rm {esc}}^{\rm {Ly\alpha }}$, with $f_{\rm {esc}}^{\rm {Ly\alpha }}$ increasing from $f_{\rm {esc}}^{\rm {Ly\alpha }}\simeq 0.04$ at $W_{\rm {\lambda }}(\rm {Ly\, \alpha })=10$ Å to $f_{\rm {esc}}^{\rm {Ly\alpha }}\simeq 0.1$ at $W_{\rm {\lambda }}(\rm {Ly\, \alpha })=25$ Å. For the first time at z ≃ 4–5, we investigate the relationship between $f_{\rm {esc}}^{\rm {Ly\alpha }}$ and $f_{\rm {esc}}^{\rm {LyC}}$ using $f_{\rm {esc}}^{\rm {LyC}}$ estimates derived using the equivalent widths of low-ionization, far-ultraviolet absorption lines in composite VANDELS spectra. Our results indicate that $f_{\rm {esc}}^{\rm {LyC}}$ rises monotonically with $f_{\rm {esc}}^{\rm {Ly\alpha }}$, following a relation of the form $f_{\rm {esc}}^{\rm {LyC}}$$\simeq 0.15^{+0.06}_{-0.04}$$f_{\rm {esc}}^{\rm {Ly\alpha }}$. Based on composite spectra of sub-samples with approximately constant Wλ(Lyα), but widely different $f_{\rm {esc}}^{\rm {Ly\alpha }}$, we demonstrate that the $f_{\rm {esc}}^{\rm {LyC}}$−$f_{\rm {esc}}^{\rm {Ly\alpha }}$correlation is not driven by a secondary correlation between $f_{\rm {esc}}^{\rm {Ly\alpha }}$ and Wλ(Lyα). The observed $f_{\rm {esc}}^{\rm {LyC}}$−$f_{\rm {esc}}^{\rm {Ly\alpha }}$ correlation is in good qualitative agreement with theoretical predictions and provides further evidence that estimates of $f_{\rm {esc}}^{\rm {LyC}}$ within the Epoch of Reionization should be based on proxies sensitive to neutral gas density/geometry and dust attenuation.
Aims.
We investigate the production efficiency of ionizing photons (
ξ
ion
∗
) of 1174 galaxies with secure redshift at
z
= 2 − 5 from the VANDELS survey to determine the relation between ionizing ...emission and physical properties of bright and massive sources.
Methods.
We constrained
ξ
ion
∗
and galaxy physical parameters by means of spectrophotometric fits performed with the
BEAGLE
code. The analysis exploits the multi-band photometry in the VANDELS fields and the measurement of UV rest-frame emission lines (CIII
λ
1909, HeII
λ
1640, and OIII
λ
1666) from deep VIMOS spectra.
Results.
We find no clear evolution of
ξ
ion
∗
with redshift within the probed range. The ionizing efficiency slightly increases at fainter
M
UV
and bluer UV slopes, but these trends are less evident when the analysis is restricted to a complete subsample at log(
M
star
/
M
⊙
) > 9.5. We find a significant trend of increasing
ξ
ion
∗
with increasing EW(Ly
α
), with an average log(
ξ
ion
∗
/Hz erg
−1
) > 25 at EW > 50 Å and a higher ionizing efficiency for high-EW CIII
λ
1909 and OIII
λ
1666 emitters. The most significant correlations are found with respect to stellar mass, specific star formation rate (sSFR), and SFR surface density (Σ
SFR
). The relation between
ξ
ion
∗
and sSFR increases monotonically from log(
ξ
ion
∗
/Hz erg
−1
)∼24.5 at log(sSFR) ∼ −9.5 yr
−1
to ∼25.5 at log(sSFR) ∼ −7.5 yr
−1
. This relation has a low scatter and only a weak dependence on mass. The objects above the main sequence of star formation consistently have higher than average
ξ
ion
∗
. A clear increase in
ξ
ion
∗
with Σ
SFR
is also found, with log(
ξ
ion
∗
/Hz erg
−1
) > 25 for objects at Σ
SFR
> 10
M
⊙
yr
−1
kpc
−2
.
Conclusions.
Bright (
M
UV
≲ 20) and massive (log(
M
star
/
M
⊙
)≳9.5) galaxies at
z
= 2 − 5 have a moderate ionizing efficiency. However, the correlation between
ξ
ion
∗
and sSFR, together with the known increase in the average sSFR with redshift at fixed stellar mass, suggests that similar galaxies in the epoch of reionization can be efficient sources of ionizing photons. The availability of sSFR and Σ
SFR
as proxies for
ξ
ion
∗
can be fundamentally important in determining the role of galaxy populations at
z
≳ 10 that were recently discovered by the
James Webb
Space Telescope in the onset of reionization.
ABSTRACT
We present the results of a new study investigating the relationship between observed Ly α equivalent width (Wλ(Ly α)) and the metallicity of the ionizing stellar population ( Z⋆) for a ...sample of 768 star-forming galaxies at 3 ≤ z ≤ 5 drawn from the VANDELS survey. Dividing our sample into quartiles of rest-frame Wλ(Ly α) across the range $-58 \,\rm {\mathring{\rm A}} \lesssim$Wλ(Ly α) $\lesssim 110 \,\rm {\mathring{\rm A}}$, we determine Z⋆ from full spectral fitting of composite far-ultraviolet spectra and find a clear anticorrelation between Wλ(Ly α) and Z⋆. Our results indicate that Z⋆ decreases by a factor ≳ 3 between the lowest Wλ(Ly α) quartile (〈Wλ(Ly α)$\rangle =-18\,\rm {\mathring{\rm A}}$) and the highest Wλ(Ly α) quartile (〈Wλ(Ly α)$\rangle =24\,\rm {\mathring{\rm A}}$). Similarly, galaxies typically defined as Lyman alpha emitters (LAEs; Wλ(Ly α) $\gt 20\,\rm {\mathring{\rm A}}$) are, on average, metal poor with respect to the non-LAE galaxy population (Wλ(Ly α) $\le 20\,\rm {\mathring{\rm A}}$) with Z⋆non-LAE ≳ 2 × Z⋆LAE. Finally, based on the best-fitting stellar models, we estimate that the increasing strength of the stellar ionizing spectrum towards lower Z⋆ is responsible for ${\simeq}15{-}25{{\ \rm per\ cent}}$ of the observed variation in Wλ(Ly α) across our sample, with the remaining contribution (${\simeq}75{-}85{{\ \rm per\ cent}}$) being due to a decrease in the H i/dust covering fractions in low- Z⋆ galaxies.
The chemical enrichment of dust and metals are vital processes in constraining the star formation history of the universe. These are important ingredients in the formation and evolution of galaxies ...overall. Previously, the dust masses of high-redshift star-forming galaxies have been determined through their far-infrared continuum, however, equivalent, and potentially simpler, approaches to determining the metal masses have yet to be explored at
z
≳ 2. Here, we present a new method of inferring the metal mass in the interstellar medium (ISM) of galaxies out to
z
≈ 8, using the far-infrared C
II
−158 μm emission line as a proxy. We calibrated the C
II
-to-
M
Z
, ISM
conversion factor based on a benchmark observational sample at
z
≈ 0, in addition to gamma-ray burst sightlines at
z
> 2 and cosmological hydrodynamical simulations of galaxies at
z
≈ 0 and
z
≈ 6. We found a universal scaling across redshifts of log(
M
Z
, ISM
/
M
⊙
) = log(
L
CII
/
L
⊙
)−0.45, with a 0.4 dex scatter, which is constant over more than two orders of magnitude in metallicity. We applied this scaling to recent surveys for C
II
in galaxies at
z
≳ 2 and compared their inferred
M
Z
, ISM
to their stellar mass (
M
⋆
). In particular, we determined the fraction of metals retained in the gas-phase ISM,
M
Z
, ISM
/
M
⋆
, as a function of redshift and we showed that an increasing fraction of metals reside in the ISM of galaxies at higher redshifts. We place further constraints on the cosmic metal mass density in the ISM (Ω
Z
, ISM
) at
z
≈ 5 and ≈7 based on recent estimates of the C
II
−158 μm luminosity functions at these epochs, yielding Ω
Z
,ISM
= 6.6
−4.3
+13
× 10
−7
M
⊙
Mpc
−3
(
z
≈ 5) and Ω
Z
,ISM
= 2.0
−1.3
+3.5
× 10
−7
M
⊙
Mpc
−3
(
z
≈ 7), respectively. These results are consistent with the expected metal yields from the integrated star formation history at the respective redshifts. This suggests that the majority of metals produced at
z
≳ 5 are confined to the ISM, with strong implications that disfavor efficient outflow processes at these redshifts. Instead, these results suggest that the extended C
II
halos predominantly trace the extended neutral gas reservoirs of high-
z
galaxies.
We have discovered a highly significant overdensity of galaxies at z = 2.300 c 0.015 in the course of a redshift survey designed to select star-forming galaxies in the redshift range z = 2.3 c 0.4 in ...the field of the bright z = 2.72 QSO HS 1700+643. The structure has a redshift-space galaxy overdensity of d super(z) sub(g) 7 and an estimated matter overdensity in real space of d sub(m) 1.8, indicating that it will virialize by z 6 0 with a mass scale of 1.4 x 10 super(15) M sub( ), that of a rich galaxy cluster. Detailed modeling of the spectral energy distribution--from the rest-frame far-UV to the rest-frame near-IR--of the 72 spectroscopically confirmed galaxies in this field for which we have obtained K sub(s) and Spitzer IRAC photometry allows for a first direct comparison of galaxy properties as a function of large-scale environment at high redshift. We find that galaxies in the protocluster environment have mean stellar masses and inferred ages that are 62 times larger (at z = 2.30) than identically UV-selected galaxies outside of the structure, and we show that this is consistent with simple theoretical expectations for the acceleration of structure formation in a region that is overdense on large scales by the observed amount. The protocluster environment contains a significant number of galaxies that already appear old, with large stellar masses (>10 super(11) M sub( )), by z = 2.3.
We use a sample of rest-frame UV-selected and spectroscopically observed galaxies at redshifts 1.9 less than or equal to z < 3.4, combined with ground-based spectroscopic Ha and Spitzer MIPS 24 mu m ...data, to derive the most robust measurements of the rest-frame UV, H alpha , and infrared (IR) luminosity functions (LFs) at these redshifts. Our sample is by far the largest of its kind, with over 2000 spectroscopic redshifts in the range 1.9 less than or equal to z < 3.4 and similar to 15,000 photometric candidates in 29 independent fields covering a total area of almost a square degree. Our method for computing the LFs takes into account a number of systematic effects, including photometric scatter, Ly alpha line perturbations to the observed optical colors of galaxies, and contaminants. Taking into account the latter, we find no evidence for an excess of UV-bright galaxies over what was inferred in early z similar to 3 LBG studies. The UV LF appears to undergo little evolution between z similar to 4 and z similar to 2. Corrected for extinction, the UV luminosity density (LD) at z similar to 2 is at least as large as the value at z similar to 3 and a factor of similar to 9 larger than the value at z similar to 6, primarily reflecting an increase in the number density of bright galaxies between z similar to 6 and z similar to 2. Our analysis yields the first constraints anchored by extensive spectroscopy on the infrared and bolometric LFs for faint and moderately luminous (L sub(bol) unk 10 super(12) L unk) galaxies. Adding the IR to the emergent UV luminosity, incorporating independent measurements of the LD from ULIRGs, and assuming realistic dust attenuation values for UV-faint galaxies, indicates that galaxies with L sub(bol) < 10 super(12) L unk account for approximately 80% of the bolometric LD and SFRD at z similar to 2 3. This suggests that previous estimates of the faint end of the L sub(bol) LF may have underestimated the steepness of the faint-end slope at L sub(bol) < 10 super(12) L unk. Our multiwavelength constraints on the global SFRD indicate that approximately one-third of the present-day stellar mass density was formed in subultraluminous galaxies between redshifts z = 1.9 3.4.
We present the results of a spectroscopic survey with LRIS-B on Keck of more than 280 star-forming galaxies and AGNs at redshifts 1.4 z 3.0 in the GOODS-N field. Candidates are selected by their U ...sub(n)GR colors using the "BM/BX" criteria to target redshift 1.4 z 2.5 galaxies and the LBG criteria to target redshift z 6 3 galaxies; combined these samples account for 625%-30% of the R and K sub(s) band counts to R = 25.5 and K sub(s)(AB) = 24.4, respectively. The 212 BM/BX galaxies and 74 LBGs constitute the largest spectroscopic sample of galaxies at z > 1.4 in GOODS-N. Extensive multiwavelength data allow us to investigate the stellar populations, stellar masses, bolometric luminosities (L sub(bol)), and extinction of z 6 2 galaxies. Deep Chandra and Spitzer data indicate that the sample includes galaxies with a wide range in L sub(bol) ( 10 super(10) to >10 super(12) L sub( )) and 4 orders of magnitude in dust obscuration (L sub(bol)/L sub(UV)). The sample includes galaxies with a large dynamic range in evolutionary state, from very young galaxies (ages 650 Myr) with small stellar masses (M* 10 super(9) M sub( )) to evolved galaxies with stellar masses comparable to the most massive galaxies at these redshifts (M* > 10 super(11) M sub( )). Spitzer data indicate that the optical sample includes some fraction of the obscured AGN population at high redshifts: at least 3 of 11 AGNs in the z > 1.4 sample are undetected in the deep X-ray data but exhibit power-law SEDs longward of 62 km (rest frame) indicative of obscured AGNs. The results of our survey indicate that rest-frame UV selection and spectroscopy presently constitute the most timewise efficient method of culling large samples of high-redshift galaxies with a wide range in intrinsic properties, and the data presented here will add significantly to the multiwavelength legacy of GOODS.
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