We investigate the relation between star formation rate (SFR) and stellar mass (M), i.e., the main sequence (MS) relation of star-forming galaxies, at in the first four Hubble Space Telescope (HST) ...Frontier Fields, on the basis of rest-frame UV observations. Gravitational lensing combined with deep HST observations allows us to extend the analysis of the MS down to at and at higher redshifts, a factor of ∼10 below most previous results. We perform an accurate simulation to take into account the effect of observational uncertainties and correct for the Eddington bias. This step allows us to reliably measure the MS and in particular its slope. While the normalization increases with redshift, we fit an unevolving and approximately linear slope. We nicely extend to lower masses the results of brighter surveys. Thanks to the large dynamic range in mass and by making use of the simulation, we analyzed any possible mass dependence of the dispersion around the MS. We find tentative evidence that the scatter decreases with increasing mass, suggesting a larger variety of star formation histories in low-mass galaxies. This trend agrees with theoretical predictions and is explained as either a consequence of the smaller number of progenitors of low-mass galaxies in a hierarchical scenario and/or of the efficient but intermittent stellar feedback processes in low-mass halos. Finally, we observe an increase in the SFR per unit stellar mass with redshift milder than predicted by theoretical models, implying a still incomplete understanding of the processes responsible for galaxy growth.
Dust plays an important role in our understanding of the Universe, but it is not obvious yet how the dust in the distant universe was formed. I derived the dust yields per asymptotic giant branch ...(AGB) star and per supernova (SN) required to explain dust masses of galaxies at z = 6.3–7.5 (680–850 million years after the Big Bang) for which dust emission has been detected (HFLS3 at z = 6.34, ULAS J1120+0641 at z = 7.085, and A1689-zD1 at z = 7.5), or unsuccessfully searched for. I found very high required yields, implying that AGB stars could not contribute substantially to dust production at these redshifts, and that SNe could explain these dust masses, but only if they do not destroy most of the dust they form (which is unlikely given the upper limits on the SN dust yields derived for galaxies where dust is not detected). This suggests that the grain growth in the interstellar medium is likely required at these early epochs.
Abstract
The Herschel Space Observatory has revealed a very different galaxyscape from that shown by optical surveys which presents a challenge for galaxy-evolution models. The Herschel surveys ...reveal (1) that there was rapid galaxy evolution in the very recent past and (2) that galaxies lie on a single Galaxy Sequence (GS) rather than a star-forming ‘main sequence’ and a separate region of ‘passive’ or ‘red-and-dead’ galaxies. The form of the GS is now clearer because far-infrared surveys such as the Herschel ATLAS pick up a population of optically red star-forming galaxies that would have been classified as passive using most optical criteria. The space-density of this population is at least as high as the traditional star-forming population. By stacking spectra of H-ATLAS galaxies over the redshift range 0.001 < z < 0.4, we show that the galaxies responsible for the rapid low-redshift evolution have high stellar masses, high star-formation rates but, even several billion years in the past, old stellar populations – they are thus likely to be relatively recent ancestors of early-type galaxies in the Universe today. The form of the GS is inconsistent with rapid quenching models and neither the analytic bathtub model nor the hydrodynamical EAGLE simulation can reproduce the rapid cosmic evolution. We propose a new gentler model of galaxy evolution that can explain the new Herschel results and other key properties of the galaxy population.
Abstract
Fast radio bursts (FRBs) are enigmatic transients with very short radio emission. Their nature is still widely debated. I provide the first analysis of atomic gas properties of a small ...sample of FRB hosts to constrain their nature. H
i
observations exist for NGC 3252, the host of FRB 181030A, M81, the host of FRB 200120E, and the Milky Way, the host of FRB 200428. I report three observables: (i) all three FRB hosts are interacting galaxies; (ii) the H
i
spectra of both FRB hosts with such data available are highly asymmetric, several standard deviations above the general population of galaxies; (iii) two FRB hosts have normal atomic gas properties and one is strongly deficient in atomic gas. This indicates that nearby and repeating FRBs are connected with a recent enhancement of star formation due to interaction. This supports fast FRB channels, for example, a massive star with a short delay time so that interaction signatures giving rise to the birth of the progenitor are still visible. Long gamma-ray burst (GRB) and broad-lined type Ic supernova (SN) hosts exhibit much more symmetric spectra, even though they were claimed to experience gas inflow from the intergalactic medium. The difference can be explained by the interactions experienced by FRB hosts being more disruptive than these gas inflows, or by the mass effect, with GRB/SN hosts at lower masses having less organized gas motions, so with H
i
lines closer to a symmetrical Gaussian. This also suggests that the emission mechanisms of FRBs and GRBs are different.
We report the detection and mapping of atomic hydrogen in H i 21 cm emission from ESO 184-G82, the host galaxy of the gamma-ray burst 980425. This is the first instance where H i in emission has been ...detected from a galaxy hosting a gamma-ray burst (GRB). ESO 184-G82 is an isolated galaxy and contains a Wolf–Rayet region close to the location of the GRB and the associated supernova, SN 1998bw. This is one of the most luminous H ii regions identified in the local Universe, with a very high inferred density of star formation. The H i 21 cm observations reveal a high H i mass for the galaxy, twice as large as the stellar mass. The spatial and velocity distribution of the H i 21 cm emission reveals a disturbed rotating gas disc, which suggests that the galaxy has undergone a recent minor merger that disrupted its rotation. We find that the Wolf–Rayet region and the GRB are both located in the highest H i column density region of the galaxy. We speculate that the merger event has resulted in shock compression of the gas, triggering extreme star formation activity, and resulting in the formation of both the Wolf–Rayet region and the GRB. The high H i column density environment of the GRB is consistent with the high H i column densities seen in absorption in the host galaxies of high-redshift GRBs.
The existence of submillimeter-selected galaxies (SMGs) at redshifts z > 4 has recently been confirmed. Simultaneously using all the available data from UV to radio, we have modeled the spectral ...energy distributions of the six known spectroscopically confirmed SMGs at z > 4. We find that their star formation rates (average {approx}2500M{sub sun} yr{sup -1}), stellar ({approx}3.6 x 10{sup 11} M{sub sun}) and dust ({approx}6.7 x 10{sup 8} M{sub sun}) masses, extinction (A{sub V} {approx} 2.2 mag), and gas-to-dust ratios ({approx}60) are within the ranges for 1.7 < z < 3.6 SMGs. Our analysis suggests that infrared-to-radio luminosity ratios of SMGs do not change up to redshift {approx}5 and are lower by a factor of {approx}2.1 than the value corresponding to the local IR-radio correlation. However, we also find dissimilarities between z > 4 and lower-redshift SMGs. Those at z > 4 tend to be among the most star-forming, least massive, and hottest ({approx}60 K) SMGs and exhibit the highest fraction of stellar mass formed in the ongoing starburst ({approx}45%). This indicates that at z > 4 we see earlier stages of evolution of submillimeter-bright galaxies. Using the derived properties for z > 4 SMGs, we investigate the origin of dust at epochs less than 1.5 Gyr after the big bang. This is significant to our understanding of the evolution of the early universe. For three z > 4 SMGs, asymptotic giant branch stars could be the dominant dust producers. However, for the remaining three only supernovae (SNe) are efficient and fast enough to be responsible for dust production, though requiring a very high dust yield per SN (0.15-0.65 M{sub sun}). The required dust yields are lower if a top-heavy initial mass function or significant dust growth in the interstellar medium is assumed. We estimate lower limits of the contribution of SMGs to the cosmic star formation and stellar mass densities at z {approx} 4-5 to be {approx}4% and {approx}1%, respectively.
Abstract
We present spatially resolved morphological properties of C
II
158
μ
m, O
III
88
μ
m, dust, and rest-frame ultraviolet (UV) continuum emission for A1689-zD1, a strongly lensed, sub-L* ...galaxy at
z
= 7.13, by utilizing deep Atacama Large Millimeter/submillimeter Array (ALMA) and Hubble Space Telescope (HST) observations. While the O
III
line and UV continuum are compact, the C
II
line is extended up to a radius of
r
∼ 12 kpc. Using multi-band rest-frame far-infrared continuum data ranging from 52 to 400
μ
m, we find an average dust temperature and emissivity index of
T
dust
=
41
−
14
+
17
K and
β
=
1.7
−
0.7
+
1.1
, respectively, across the galaxy. We find slight differences in the dust continuum profiles at different wavelengths, which may indicate that the dust temperature decreases with distance. We map the star formation rate (SFR) via IR and UV luminosities and determine a total SFR of 37 ± 1
M
⊙
yr
−1
with an obscured fraction of 87%. While the O
III
line is a good tracer of the SFR, the C
II
line shows deviation from the local
L
C
II
-SFR relations in the outskirts of the galaxy. Finally, we observe a clear difference in the line profile between C
II
and O
III
, with significant residuals (∼5
σ
) in the O
III
line spectrum after subtracting a single Gaussian model. This suggests a possible origin of the extended C
II
structure from the cooling of hot ionized outflows. The extended C
II
and high-velocity O
III
emission may both contribute in part to the high
L
O
III
/
L
C
II
ratios recently reported in
z
> 6 galaxies.
Long-duration gamma-ray bursts (GRBs) are powerful tracers of star-forming galaxies. We have defined a homogeneous sub-sample of 69 Swift GRB-selected galaxies spanning a very wide redshift range. ...Special attention has been devoted to making the sample optically unbiased through simple and well-defined selection criteria based on the high-energy properties of the bursts and their positions on the sky. In this paper, we present the survey design and summarize the results of our observing program conducted at the ESO Very Large Telescope (VLT) aimed at obtaining the most basic properties of galaxies in this sample, including a catalog of R and Ksubs magnitudes and redshifts. Seven hosts have detections of the Ly alpha emission line and we can exclude an early indication that Ly alpha emission is ubiquitous among GRB hosts, but confirm that Ly alpha is stronger in GRB-selected galaxies than in flux-limited samples of Lyman break galaxies.
Abstract
We report the detection of a massive neutral gas outflow in the
z
= 2.09 gravitationally lensed dusty star-forming galaxy HATLAS J085358.9+015537 (G09v1.40), seen in absorption with the OH
+
...(1
1
−1
0
) transition using spatially resolved (0.″5 × 0.″4) Atacama Large Millimeter/submillimeter Array (ALMA) observations. The blueshifted OH
+
line is observed simultaneously with the CO(9−8) emission line and underlying dust continuum. These data are complemented by high-angular-resolution (0.″17 × 0.″13) ALMA observations of CH
+
(1−0) and underlying dust continuum, and Keck 2.2
μ
m imaging tracing the stellar emission. The neutral outflow, dust, dense molecular gas, and stars all show spatial offsets from each other. The total atomic gas mass of the observed outflow is 6.7 × 10
9
M
⊙
, >25% as massive as the gas mass of the galaxy. We find that a conical outflow geometry best describes the OH
+
kinematics and morphology and derive deprojected outflow properties as functions of possible inclination (0.°38–64°). The neutral gas mass outflow rate is between 83 and 25,400
M
⊙
yr
−1
, exceeding the star formation rate (788 ± 300
M
⊙
yr
−1
) if the inclination is >3.°6 (mass-loading factor = 0.3–4.7). Kinetic energy and momentum fluxes span (4.4–290) × 10
9
L
⊙
and (0.1–3.7) × 10
37
dyne, respectively (energy-loading factor = 0.013–16), indicating that the feedback mechanisms required to drive the outflow depend on the inclination assumed. We derive a gas depletion time between 29 and 1 Myr, but find that the neutral outflow is likely to remain bound to the galaxy unless the inclination is small and may be reaccreted if additional feedback processes do not occur.
Galaxy interactions are often accompanied by an enhanced star formation rate (SFR). Since molecular gas is essential for star formation, it is vital to establish whether and by how much galaxy ...interactions affect the molecular gas properties. We investigate the effect of interactions on global molecular gas properties by studying a sample of 58 galaxies in pairs and 154 control galaxies. Molecular gas properties are determined from observations with the JCMT, PMO, and CSO telescopes and supplemented with data from the xCOLD GASS and JINGLE surveys at 12CO(1-0) and 12CO(2-1). The SFR, gas mass ( ), and gas fraction (fgas) are all enhanced in galaxies in pairs by ∼2.5 times compared to the controls matched in redshift, mass, and effective radius, while the enhancement of star formation efficiency (SFE SFR/ ) is less than a factor of 2. We also find that the enhancements in SFR, and fgas, increase with decreasing pair separation and are larger in systems with smaller stellar mass ratio. Conversely, the SFE is only enhanced in close pairs (separation <20 kpc) and equal-mass systems; therefore, most galaxies in pairs lie in the same parameter space on the SFR- plane as controls. This is the first time that the dependence of molecular gas properties on merger configurations is probed statistically with a relatively large sample and a carefully selected control sample for individual galaxies. We conclude that galaxy interactions do modify the molecular gas properties, although the strength of the effect is dependent on merger configuration.
PDF
