A merger in the dusty, z = 7.5 galaxy A1689-zD1? Knudsen, Kirsten K; Watson, Darach; Frayer, David ...
Monthly notices of the Royal Astronomical Society,
04/2017, Letnik:
466, Številka:
1
Journal Article
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Abstract
The gravitationally lensed galaxy A1689-zD1 is one of the most distant spectroscopically confirmed sources (z = 7.5). It is the earliest known galaxy where the interstellar medium (ISM) has ...been detected; dust emission was detected with the Atacama Large Millimetre Array (ALMA). A1689-zD1 is also unusual among high-redshift dust emitters as it is a sub-L
★ galaxy and is therefore a good prospect for the detection of gaseous ISM in a more typical galaxy at this redshift. We observed A1689-zD1 with ALMA in bands 6 and 7 and with the Green Bank Telescope (GBT) in band Q. To study the structure of A1689-zD1, we map the mm-thermal dust emission and find two spatial components with sizes about 0.4 − 1.7 kpc (lensing-corrected). The rough spatial morphology is similar to what is observed in the near-infrared with HST and points to a perturbed dynamical state, perhaps indicative of a major merger or a disc in early formation. The ALMA photometry is used to constrain the far-infrared spectral energy distribution, yielding a dust temperature (T
dust ∼ 35–45 K for β = 1.5 − 2). We do not detect the CO(3-2) line in the GBT data with a 95 per cent upper limit of 0.3 mJy observed. We find a slight excess emission in ALMA band 6 at 220.9 GHz. If this excess is real, it is likely due to emission from the C ii 158.8 μm line at
$z_{\rm C\,\small {II}} = 7.603$
. The stringent upper limits on the C ii L
FIR luminosity ratio suggest a C ii deficit similar to several bright quasars and massive starbursts.
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.
There is a remarkably tight relation between the observationally inferred dust masses and star-formation rates (SFRs) of Sloan Digital Sky Survey galaxies, M dust ∝ SFR 1.11(exp). Here we extend the ...M dust-SFR relation to the high end and show that it bends over at very large SFRs (i.e., dust masses are lower than predicted for a given SFR). We identify several distinct evolutionary processes in the diagram: (1) a star-bursting phase in which dust builds up rapidly at early times. The maximum attainable dust mass in this process is the cause of the bend-over of the relation. A high dust-formation efficiency, a bottom-light initial mass function, and negligible supernova shock dust destruction are required to produce sufficiently high dust masses. (2) A quiescent star-forming phase in which the subsequent parallel decline in dust mass and SFR gives rise to the M dust-SFR relation, through astration and dust destruction. The dust-to-gas ratio is approximately constant along the relation. We show that the power-law slope of the M dust-SFR relation is inversely proportional to the global Schmidt-Kennicutt law exponent (i.e., ~0.9) in simple chemical evolution models. (3) A quenching phase which causes star formation to drop while the dust mass stays roughly constant or drops proportionally. Combined with merging, these processes, as well as the range in total baryonic mass, give rise to a complex population of the diagram which adds significant scatter to the original M dust-SFR relation. (4) At very high redshifts, a population of galaxies located significantly below the local relation is predicted.
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.
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.
We report the detection of the radio afterglow of a long gamma-ray burst (GRB) 111005A at 5-345 GHz, including very long baseline interferometry observations with a positional error of 0.2 mas. The ...afterglow position is coincident with the disc of a galaxy ESO 58049 at z = 0.01326 (∼1″ from its centre), which makes GRB 111005A the second-closest GRB known to date, after GRB 980425. The radio afterglow of GRB 111005A was an order of magnitude less luminous than those of local low-luminosity GRBs, and obviously less luminous than those of cosmological GRBs. The radio flux was approximately constant and then experienced an unusually rapid decay a month after the GRB explosion. Similarly to only two other GRBs, we did not find the associated supernovae (SNe), despite deep near- and mid-infrared observations 1-9 days after the GRB explosion, reaching ∼20 times fainter than other SNe associated with GRBs. Moreover, we measured a twice-solar metallicity for the GRB location. The low y-ray and radio luminosities, rapid decay, lack of a SN, and super-solar metallicity suggest that GRB 111005A represents a rare class of GRB that is different from typical core-collapse events. We modelled the spectral energy distribution of the GRB 111005A host finding that it is a moderately star-forming dwarf galaxy, similar to the host of GRB 980425. The existence of two local GRBs in such galaxies is still consistent with the hypothesis that the GRB rate is proportional to the cosmic star formation rate (SFR) density, but suggests that the GRB rate is biased towards low SFRs. Using the far-infrared detection of ESO 580-49, we conclude that the hosts of both GRBs 111005A and 980425 exhibit lower dust content than what would be expected from their stellar masses and optical colors.
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
We study the dust properties of 192 nearby galaxies from the JINGLE survey using photometric data in the 22–850 $\mu$m range. We derive the total dust mass, temperature T, and emissivity ...index β of the galaxies through the fitting of their spectral energy distribution (SED) using a single modified blackbody model (SMBB). We apply a hierarchical Bayesian approach that reduces the known degeneracy between T and β. Applying the hierarchical approach, the strength of the T–β anticorrelation is reduced from a Pearson correlation coefficient R = −0.79 to R = −0.52. For the JINGLE galaxies we measure dust temperatures in the range 17−30 K and dust emissivity indices β in the range 0.6−2.2. We compare the SMBB model with the broken emissivity law modified blackbody (BMBB) and the two modified blackbody (TMBB) models. The results derived with the SMBB and TMBB are in good agreement, thus applying the SMBB, which comes with fewer free parameters, does not penalize the measurement of the cold dust properties in the JINGLE sample. We investigate the relation between T and β and other global galaxy properties in the JINGLE and Herschel Reference Survey (HRS) sample. We find that β correlates with the stellar mass surface density (R = 0.62) and anticorrelates with the H i mass fraction (MH i/M*, R = −0.65), whereas the dust temperature correlates strongly with the star formation rate normalized by the dust mass (R = 0.73). These relations can be used to estimate T and β in galaxies with insufficient photometric data available to measure them directly through SED fitting.
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.
ABSTRACT
We present an analysis of a new 120 deg2 radio continuum image of the Large Magellanic Cloud (LMC) at 888 MHz with a bandwidth of 288 MHz and beam size of ...13${_{.}^{\prime\prime}}$9 × 12${_{.}^{\prime\prime}}$1 from the Australian Square Kilometre Array Pathfinder processed as part of the Evolutionary Map of the Universe survey. The median root mean squared noise is 58 $\mu$Jy beam−1. We present a catalogue of 54 612 sources, divided over a Gold list (30 866 sources) complete down to 0.5 mJy uniformly across the field, a Silver list (22 080 sources) reaching down to <0.2 mJy, and a Bronze list (1666 sources) of visually inspected sources in areas of high noise and/or near bright complex emission. We discuss detections of planetary nebulae and their radio luminosity function, young stellar objects showing a correlation between radio luminosity and gas temperature, novae and X-ray binaries in the LMC, and active stars in the Galactic foreground that may become a significant population below this flux level. We present examples of diffuse emission in the LMC (H ii regions, supernova remnants, bubbles) and distant galaxies showcasing spectacular interaction between jets and intracluster medium. Among 14 333 infrared counterparts of the predominantly background radio source population, we find that star-forming galaxies become more prominent below 3 mJy compared to active galactic nuclei. We combine the new 888 MHz data with archival Australia Telescope Compact Array data at 1.4 GHz to determine spectral indices; the vast majority display synchrotron emission but flatter spectra occur too. We argue that the most extreme spectral index values are due to variability.
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