Abstract
We present the “SINS/zC-SINF AO survey” of 35 star-forming galaxies, the largest sample with deep adaptive optics (AO)–assisted near-infrared integral field spectroscopy at
z
∼ 2. The ...observations, taken with SINFONI at the Very Large Telescope, resolve the H
α
and N
ii
emission and kinematics on scales of ∼1.5 kpc. The sample probes the massive (
M
⋆
∼ 2 × 10
9
− 3 × 10
11
M
⊙
), actively star-forming (SFR ∼ 10–600
M
⊙
yr
−1
) part of the
z
∼ 2 galaxy population over a wide range of colors ((
U
−
V
)
rest
∼ 0.15–1.5 mag) and half-light radii (
R
e,H
∼ 1–8.5 kpc). The sample overlaps largely with the “main sequence” of star-forming galaxies in the same redshift range to a similar
K
AB
= 23 mag limit; it has ∼0.3 dex higher median specific SFR, ∼0.1 mag bluer median (
U
−
V
)
rest
color, and ∼10% larger median rest-optical size. We describe the observations, data reduction, and extraction of basic flux and kinematic properties. With typically 3–4 times higher resolution and 4–5 times longer integrations (up to 23 hr) than the seeing-limited data sets of the same objects, the AO data reveal much more detail in morphology and kinematics. The complete AO observations confirm the majority of kinematically classified disks and the typically elevated disk velocity dispersions previously reported based on subsets of the data. We derive typically flat or slightly negative radial N
ii
/
gradients, with no significant trend with global galaxy properties, kinematic nature, or the presence of an AGN. Azimuthal variations in N
ii
/
are seen in several sources and are associated with ionized gas outflows and possibly more metal-poor star-forming clumps or small companions. The reduced AO data are made publicly available (
http://www.mpe.mpg.de/ir/SINS/SINS-zcSINF-data
).
We present the Spectroscopic Imaging survey in the near-infrared (near-IR) with SINFONI (SINS) of high-redshift galaxies. With 80 objects observed and 63 detected in at least one rest-frame optical ...nebular emission line, mainly H Delta *a, SINS represents the largest survey of spatially resolved gas kinematics, morphologies, and physical properties of star-forming galaxies at z ~ 1-3. We describe the selection of the targets, the observations, and the data reduction. We then focus on the 'SINS H Delta *a sample,' consisting of 62 rest-UV/optically selected sources at 1.3 < z < 2.6 for which we targeted primarily the H Delta *a and N II emission lines. Only 30% of this sample had previous near-IR spectroscopic observations. The galaxies were drawn from various imaging surveys with different photometric criteria; as a whole, the SINS H Delta *a sample covers a reasonable representation of massive M 1010 M star-forming galaxies at z 1.5-2.5, with some bias toward bluer systems compared to pure K-selected samples due to the requirement of secure optical redshift. The sample spans 2 orders of magnitude in stellar mass and in absolute and specific star formation rates, with median values 3 X 1010 M, 70 M yr-1, and 3 Gyr-1. The ionized gas distribution and kinematics are spatially resolved on scales ranging from 1.5 kpc for adaptive optics assisted observations to typically 4-5 kpc for seeing-limited data. The H Delta *a morphologies tend to be irregular and/or clumpy. About one-third of the SINS H Delta *a sample galaxies are rotation-dominated yet turbulent disks, another one-third comprises compact and velocity dispersion-dominated objects, and the remaining galaxies are clear interacting/merging systems; the fraction of rotation-dominated systems increases among the more massive part of the sample. The H Delta *a luminosities and equivalent widths suggest on average roughly twice higher dust attenuation toward the H II regions relative to the bulk of the stars, and comparable current and past-averaged star formation rates.
ABSTRACT We present U336V606J125H160 follow-up Hubble Space Telescope (HST) observations of 16 z ∼ 3 candidate Lyman continuum (LyC) emitters in the HS1549+1919 field. With these data, we obtain high ...spatial-resolution photometric redshifts of all sub-arcsecond components of the LyC candidates in order to eliminate foreground contamination and identify robust candidates for leaking LyC emission. Of the 16 candidates, we find one object with a robust LyC detection that is not due to foreground contamination. This object (MD5) resolves into two components; we refer to the LyC-emitting component as MD5b. MD5b has an observed 1500 to 900 flux-density ratio of , compatible with predictions from stellar population synthesis models. Assuming minimal IGM absorption, this ratio corresponds to a relative (absolute) escape fraction of = 75%-100% ( = 14%-19%). The stellar population fit to MD5b indicates an age of 50 Myr, which is in the youngest 10% of the HST sample and the youngest third of typical z ∼ 3 Lyman break galaxies, and may be a contributing factor to its LyC detection. We obtain a revised, contamination-free estimate for the comoving specific ionizing emissivity at z = 2.85, indicating (with large uncertainties) that star-forming galaxies provide roughly the same contribution as QSOs to the ionizing background at this redshift. Our results show that foreground contamination prevents ground-based LyC studies from obtaining a full understanding of LyC emission from z ∼ 3 star-forming galaxies. Future progress in direct LyC searches is contingent upon the elimination of foreground contaminants through high spatial-resolution observations, and upon acquisition of sufficiently deep LyC imaging to probe ionizing radiation in high-redshift galaxies.
Abstract
We present a joint analysis of the galaxy S04590 at
z
= 8.496 based on NIRSpec, NIRCam, and NIRISS observations obtained as part of the Early Release Observations program of the James Webb ...Space Telescope (JWST) and the far-infrared C
ii
158
μ
m emission line detected by dedicated Atacama Large Millimeter/submillimeter Array (ALMA) observations. We determine the physical properties of S04590 from modeling of the spectral energy distribution (SED) and through the redshifted optical nebular emission lines detected with JWST/NIRSpec. The best-fit SED model reveals a low-mass (
M
⋆
= 10
7.2
–10
8
M
⊙
) galaxy with a low oxygen abundance of
12
+
log
(
O
/
H
)
=
7.16
−
0.12
+
0.10
derived from the strong nebular and auroral emission lines. Assuming that C
ii
effectively traces the interstellar medium, we estimate the total gas mass of the galaxy to be
M
gas
= (8.0 ± 4.0) × 10
8
M
⊙
based on the luminosity and spatial extent of C
ii
. This yields an exceptionally high gas fraction,
f
gas
=
M
gas
/(
M
gas
+
M
⋆
) ≳ 90%, though one still consistent with the range expected for low metallicity. We further derive the metal mass of the galaxy based on the gas mass and gas-phase metallicity, which we find to be consistent with the expected metal production from Type II supernovae. Finally, we make the first constraints on the dust-to-gas (DTG) and dust-to-metal (DTM) ratios of galaxies in the epoch of reionization at
z
≳ 6, showing overall low mass ratios of logDTG < −3.8 and logDTM < −0.5, though they are consistent with established scaling relations and in particular with those of the local metal-poor galaxy I Zwicky 18. Our analysis highlights the synergy between ALMA and JWST in characterizing the gas, metal, and stellar content of the first generation of galaxies.
We present the results of spectroscopic, narrow-band and X-ray observations of a z= 2.30 protocluster in the field of the QSO HS 1700+643. Using a sample of BX/MD galaxies, which are selected to be ...at z∼ 2.2–2.7 by their rest-frame ultraviolet colours, we find that there are five protocluster AGN which have been identified by characteristic emission-lines in their optical/near-IR spectra; this represents an enhancement over the field significant at >98.5 per cent confidence. Using a ∼200-ks Chandra/ACIS-I observation of this field we detect a total of 161 X-ray point sources to a Poissonian false-probability limit of 4 × 10−6 and identify eight of these with BX/MD galaxies. Two of these are spectroscopically confirmed protocluster members and are also classified as emission-line AGN. When compared to a similarly selected field sample, the analysis indicates this is also evidence for an enhancement of X-ray selected BX/MD AGN over the field, significant at >99 per cent confidence. Deep Lyα narrow-band imaging reveals that a total of 4/123 Lyα emitters (LAEs) are found to be associated with X-ray sources, with two of these confirmed protocluster members and one highly likely member. We do not find a significant enhancement of AGN activity in this LAE sample over that of the field (result is significant at only 87 per cent confidence). The X-ray emitting AGN fractions for the BX/MD and LAE samples are found to be 6.9+9.2−4.4 and 2.9+2.9−1.6 per cent, respectively, for protocluster AGN with L2-10 keV≥ 4.6 × 1043 erg s−1 at z= 2.30. These findings are similar to results from the z= 3.09 protocluster in the SSA 22 field found by Lehmer et al. (2009), in that both suggest AGN activity is favoured in dense environments at z > 2.
We present results from a survey for z ~ 2.85 Lyman-continuum (LyC) emission in the HS1549+1933 field and place constraints on the amount of ionizing radiation escaping from star-forming galaxies. ...Using a custom narrowband filter (NB3420) tuned to wavelengths just below the Lyman limit at z > or =, slanted 2.82, we probe the LyC spectral region of 49 Lyman break galaxies (LBGs) and 91 Ly alpha emitters (LAEs) spectroscopically confirmed at z > or =, slanted 2.82. Four LBGs and seven LAEs are detected in NB3420. We find (F sub(UV)/F sub(LyC)) sub(LBG) super(corr) = 82 + or - 45 and (F sub(UV)/F sub(LyC)) super(LAE) sub(corr ) = 7.4 + or - 3.6. In order to study the differential properties of galaxies with and without LyC detections, we analyze narrowband Ly alpha imaging and rest-frame near-infrared imaging, finding that while LAEs with Ly alpha detections have lower Ly alpha equivalent widths on average, there is no substantial difference in the rest-frame near-infrared colors of LBGs or LAEs with and without LyC detections.
ABSTRACT
We present results from the NIRVANDELS survey on the gas-phase metallicity (Zg, tracing O/H) and stellar metallicity (Z⋆, tracing Fe/H) of 33 star-forming galaxies at redshifts 2.95 < z < ...3.80. Based on a combined analysis of deep optical and near-IR spectra, tracing the rest-frame far-ultraviolet (FUV; 1200–2000 Å) and rest-frame optical (3400–5500 Å), respectively, we present the first simultaneous determination of the stellar and gas-phase mass–metallicity relationships (MZRs) at z ≃ 3.4. In both cases, we find that metallicity increases with increasing stellar mass (M⋆) and that the power-law slope at M⋆ ≲ 1010M⊙ of both MZRs scales as $Z \propto M_{\star }^{0.3}$. Comparing the stellar and gas-phase MZRs, we present direct evidence for super-solar O/Fe ratios (i.e. α-enhancement) at z > 3, finding (O/Fe) = 2.54 ± 0.38 × (O/Fe)⊙, with no clear dependence on M⋆.
Aims. Long gamma-ray bursts (LGRB) have been proposed as promising tracers of star formation owing to their association with the core-collapse of massive stars. Nonetheless, previous studies we ...carried out at z < 1 support the hypothesis that the conditions necessary for the progenitor star to produce an LGRB (e.g. low metallicity), were challenging the use of LGRBs as star-formation tracers, at least at low redshift. The goal of this work is to characterise the population of host galaxies of LGRBs at 1 < z < 2, investigate the conditions in which LGRBs form at these redshifts and assess their use as tracers of star formation. Methods. We performed a spectro-photometric analysis to determine the stellar mass, star formation rate, specific star formation rate and metallicity of the complete, unbiased host galaxy sample of the Swift/BAT6 LGRB sample at 1 < z < 2. We compared the distribution of these properties to the ones of typical star-forming galaxies from the MOSDEF and COSMOS2015 Ultra Deep surveys, within the same redshift range. Results. We find that, similarly to z < 1, LGRBs do not directly trace star formation at 1 < z < 2, and they tend to avoid high-mass, high-metallicity host galaxies. We also find evidence for an enhanced fraction of starbursts among the LGRB host sample with respect to the star-forming population of galaxies. Nonetheless we demonstrate that the driving factor ruling the LGRB efficiency is metallicity. The LGRB host distributions can be reconciled with the ones expected from galaxy surveys by imposing a metallicity upper limit of logOH ∼ 8.55. We can determine upper limits on the fraction of super-solar metallicity LGRB host galaxies of ∼20%, 10% at z < 1, 1 < z < 2, respectively. Conclusions. Metallicity rules the LGRB production efficiency, which is stifled at Z ≳ 0.7 Z⊙. Under this hypothesis we can expect LGRBs to trace star formation at z > 3, once the bulk of the star forming galaxy population are characterised by metallicities below this limit. The role played by metallicity can be explained by the conditions necessary for the progenitor star to produce an LGRB. The moderately high metallicity threshold found is in agreement with the conditions necessary to rapidly produce a fast-rotating Wolf-Rayet stars in close binary systems, and could be accommodated by single star models under chemically homogeneous mixing with very rapid rotation and weak magnetic coupling.
We study the properties of luminous stellar 'clumps' identified in deep, 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. Individual clumps contribute ~0.5%-15% of the galaxy-integrated rest-frame 5000 A emission, with median of 2%; the total contribution of clump light ranges from 10% to 25%. The median intrinsic clump size and stellar mass are ~1 kpc and ~109 M , in the ranges for clumps identified in rest-UV or line emission in other studies. The clump sizes and masses in the subset of disks are broadly consistent with expectations for clump formation through gravitational instabilities in gas-rich, turbulent disks given the host galaxies' global properties. By combining the NIC2 data with Advanced Camera for Surveys (ACS)/F814W imaging available for one source, and adaptive-optics-assisted SINFONI H Delta *a data for another, we infer modest color, M/L, and stellar age variations within each galaxy. In these two objects, sets of clumps identified at different wavelengths do not fully overlap; NIC2-identified clumps tend to be redder/older than ACS- or H Delta *a-identified clumps without rest-frame optical counterparts. There is evidence for a systematic trend of older ages at smaller galactocentric radii among the clumps, consistent with scenarios where inward migration of clumps transports material toward the central regions. From constraints on a bulge-like component at radii 1-3 kpc, none of the five disks in our sample appears to contain a compact massive stellar core, and we do not discern a trend of bulge stellar mass fraction with stellar age of the galaxy. Further observations are necessary to probe the buildup of stellar bulges and the role of clumps in this process.
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