This work presents high-precision measurements of the specific baryon angular momentum j sub(b) contained in stars, atomic gas, and molecular gas, out to gap10 scale radii, in 16 nearby spiral ...galaxies of the THINGS sample. The accuracy of these measurements improves on existing studies by an order of magnitude, leading to the discovery of a strong correlation between the baryon mass M sub(b), j sub(b), and the bulge mass fraction beta , fitted by beta = -(0.34 + or = 0.03)lg(j sub(b)M super(-1)/10 super(-7)kpc km s super(-1) M sub(middot in circle) super(1)) - (0.04 + or = 0.01) on the full sample range of 0 < or = beta lap 0.3 and 10 super(9) M sub(middot in circle) < M sub(b) < 10 super(11) M sub(middot in circle). The corresponding relation for the stellar quantities M sub(*) and j sub(*) is identical within the uncertainties. These M-j- beta relations likely originate from the proportionality between jM super(-1) and the surface density of the disk that dictates its stability against (pseudo-)bulge formation. Using a cold dark matter model, we can approximately explain classical scaling relations, such as the fundamental plane of spiral galaxies, the Tully-Fisher relation, and the mass-size relation, in terms of the M-j(- beta ) relation. These results advocate the use of mass and angular momentum as the most fundamental quantities of spiral galaxies.
Abstract
The GLASS-JWST Early Release Science (hereafter GLASS-JWST-ERS) Program will obtain and make publicly available the deepest extragalactic data of the ERS campaign. It is primarily designed ...to address two key science questions, namely, “what sources ionized the universe and when?” and “how do baryons cycle through galaxies?”, while also enabling a broad variety of first look scientific investigations. In primary mode, it will obtain NIRISS and NIRSpec spectroscopy of galaxies lensed by the foreground Hubble Frontier Field cluster, Abell 2744. In parallel, it will use NIRCam to observe two fields that are offset from the cluster center, where lensing magnification is negligible, and which can thus be effectively considered blank fields. In order to prepare the community for access to this unprecedented data, we describe the scientific rationale, the survey design (including target selection and observational setups), and present pre-commissioning estimates of the expected sensitivity. In addition, we describe the planned public releases of high-level data products, for use by the wider astronomical community.
Abstract
We train and apply convolutional neural networks, a machine learning technique developed to learn from and classify image data, to Canada–France–Hawaii Telescope Legacy Survey (CFHTLS) ...imaging for the identification of potential strong lensing systems. An ensemble of four convolutional neural networks was trained on images of simulated galaxy–galaxy lenses. The training sets consisted of a total of 62 406 simulated lenses and 64 673 non-lens negative examples generated with two different methodologies. An ensemble of trained networks was applied to all of the 171 deg2 of the CFHTLS wide field image data, identifying 18 861 candidates including 63 known and 139 other potential lens candidates. A second search of 1.4 million early-type galaxies selected from the survey catalogue as potential deflectors, identified 2465 candidates including 117 previously known lens candidates, 29 confirmed lenses/high-quality lens candidates, 266 novel probable or potential lenses and 2097 candidates we classify as false positives. For the catalogue-based search we estimate a completeness of 21–28 per cent with respect to detectable lenses and a purity of 15 per cent, with a false-positive rate of 1 in 671 images tested. We predict a human astronomer reviewing candidates produced by the system would identify 20 probable lenses and 100 possible lenses per hour in a sample selected by the robot. Convolutional neural networks are therefore a promising tool for use in the search for lenses in current and forthcoming surveys such as the Dark Energy Survey and the Large Synoptic Survey Telescope.
ABSTRACT We show that the mass fraction f atm = 1.35 M H I / M of neutral atomic gas (H i and He) in isolated local disk galaxies of baryonic mass M is well described by a straightforward stability ...model for flat exponential disks. In the outer disk parts, where gas at the characteristic dispersion of the warm neutral medium is stable in the sense of Toomre, the disk consists of neutral atomic gas; conversely, the inner part where this medium would be Toomre-unstable, is dominated by stars and molecules. Within this model, f atm only depends on a global stability parameter q j / ( GM ) , where j is the baryonic specific angular momentum of the disk and the velocity dispersion of the atomic gas. The analytically derived first-order solution f atm = min { 1 , 2.5 q 1.12 } provides a good fit to all plausible rotation curves. This model, with no free parameters, agrees remarkably well ( 0.2 dex) with measurements of f atm in isolated local disk galaxies, even with galaxies that are extremely H i-rich or H i-poor for their mass. The finding that f atm increasing monotonically with q for pure stability reasons offers a powerful intuitive explanation for the mean variation of f atm with M : in a cold dark matter universe, galaxies are expected to follow j ∝ M 2 / 3 , which implies the average scaling q ∝ M − 1 / 3 and hence f atm ∝ M − 0.37 , in agreement with the observations.
The Galaxy Population Hosting Gamma-Ray Bursts Savaglio, S; Glazebrook, K; Le Borgne, D
Astrophysical journal/The Astrophysical journal,
01/2009, Volume:
691, Issue:
1
Journal Article
Peer reviewed
Open access
We present the most extensive and complete study of the properties for the largest sample (46 objects) of gamma-ray burst (GRB) host galaxies. The redshift interval and the mean redshift of the ...sample are 0 < z < 6.3 and z = 0.96 (look-back time: 7.2 Gyr), respectively; 89% of the hosts are at z <= 1.6. Optical-near-IR (NIR) photometry and spectroscopy are used to derive stellar masses, star formation rates (SFRs), dust extinctions, and metallicities. The average stellar mass is 109.3 M , with a 1s dispersion of 0.8 dex. The average metallicity for a subsample of 17 hosts is about 1/6 solar and the dust extinction in the visual band (for a subsample of 10 hosts) is AV = 0.5. We obtain new relations to derive SFR from O II or UV fluxes, when Balmer emission lines are not available. SFRs, corrected for dust extinction, aperture-slit loss, and stellar Balmer absorption are in the range 0.01-36 M yr -1. The median SFR per unit stellar mass (specific SFR) is 0.8 Gyr -1. Equivalently the inverse quantity, the median formation timescale, is 1.3 Gyr. Most GRBs are associated with the death of young massive stars, more common in star-forming galaxies. Therefore, GRBs are an effective tool to detect star-forming galaxies in the universe. Star-forming galaxies at z < 1.6 are a faint and low-mass population, hard to detect by conventional optical-NIR surveys, unless a GRB event occurs. There is no compelling evidence that GRB hosts are peculiar galaxies. More data on the subclass of short GRB are necessary to establish the nature of their hosts.
We present Keck–MOSFIRE H and K spectra for a sample of 24 candidate quiescent galaxies at 3 < z < 4, identified from their rest-frame UVJ colors and photometric redshifts in the ZFOURGE and 3DHST ...surveys. With median integration times of one hour in H and five in K, we obtain spectroscopic redshifts for half of the sample, using either Balmer absorption lines or nebular emission lines. We confirm the high accuracy of the photometric redshifts for this spectroscopically-confirmed sample, with a median |Zphot − Zspec|/(1 + Zspec) of 1.2%. Two galaxies turn out to be dusty Hα emitters at lower redshifts (z < 2.5), and these are the only two detected in the sub-mm with ALMA. High equivalent-width O III emission is observed in two galaxies, contributing up to 30% of the K-band flux and mimicking the UVJ colors of an old stellar population. This implies a failure rate of only 20% for the UVJ selection at these redshifts. Lastly, Balmer absorption features are identified in four galaxies, among the brightest of the sample, confirming the absence of OB stars. We then modeled the spectra and photometry of all quiescent galaxies with a wide range of star-formation histories. We find specific star-formation rates (sSFR) lower than 0.15 Gyr−1 (a factor of ten below the main sequence) for all but one galaxy, and lower than 0.01 Gyr−1 for half of the sample. These values are consistent with the observed Hβ and O II luminosities, and the ALMA non-detections. The implied formation histories reveal that these galaxies have quenched on average 300 Myr prior to being observed, between z = 3.5 and 5, and that half of their stars were formed by z ∼ 5.5 with a mean SFR ~ 300 M⊙ yr−1. We finally compared the UVJ selection to a selection based instead on the sSFR, as measured from the photometry. We find that galaxies a factor of ten below the main sequence are 40% more numerous than UVJ-selected quiescent galaxies, implying that the UVJ selection is pure but incomplete. Current models fail at reproducing our observations, and underestimate either the number density of quiescent galaxies by more than an order of magnitude, or the duration of their quiescence by a factor two. Overall, these results confirm the existence of an unexpected population of quiescent galaxies at z > 3, and offer the first insights on their formation histories.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
We obtained ALMA spectroscopy and deep imaging to investigate the origin of the unexpected sub-millimeter emission toward the most distant quiescent galaxy known to date, ZF-COSMOS-20115 at z = ...3.717. We show here that this sub-millimeter emission is produced by another massive (M*~ 1011 M⊙), compact (r1∕2 = 0.67 ± 0.14 kpc) and extremely obscured galaxy (AV ~ 3.5), located only 0.43′′ (3.1 kpc) away from the quiescent galaxy. We dub the quiescent and dusty galaxies Jekyll and Hyde, respectively. No dust emission is detected at the location of the quiescent galaxy, implying SFR < 13 M⊙ yr−1 which is the most stringent upper limit ever obtained for a quiescent galaxy at these redshifts. The two sources are spectroscopically confirmed to lie at the same redshift thanks to the detection of C II158 in Hyde (z = 3.709), which provides one the few robust redshifts for a highly-obscured “H-dropout” galaxy (H − 4.5 = 5.1 ± 0.8). The C II line shows a clear rotating-disk velocity profile which is blueshifted compared to the Balmer lines of Jekyll by 549 ± 60 km s−1, demonstrating that it is produced by another galaxy. Careful de-blending of the Spitzer imaging confirms the existence of this new massive galaxy, and its non-detection in the Hubble images requires extremely red colors and strong attenuation by dust. Full modeling of the UV-to-far-IR emission of both galaxies shows that Jekyll has fully quenched at least 200Myr prior to observation and still presents a challenge for models, while Hyde only harbors moderate star-formation with SFR ≲ 120 M⊙ yr−1, and is located at least a factor 1.4 below the z ~ 4 main sequence. Hyde could also have stopped forming stars less than 200 Myr before being observed; this interpretation is also suggested by its compactness comparable to that of z ~ 4 quiescent galaxies and its low C II/FIR ratio, but significant on-going star-formation cannot be ruled out. Lastly, we find that despite its moderate SFR, Hyde hosts a dense reservoir of gas comparable to that of the most extreme starbursts. This suggests that whatever mechanism has stopped or reduced its star-formation must have done so without expelling the gas outside of the galaxy. Because of their surprisingly similar mass, compactness, environment and star-formation history, we argue that Jekyll and Hyde can be seen as two stages of the same quenching process, and provide a unique laboratory to study this poorly understood phenomenon.
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Abstract
We compare the molecular and ionized gas velocity dispersions of nine nearby turbulent disks, analogs to high-redshift galaxies, from the DYNAMO sample using new Atacama Large ...Millimeter/submillimeter Array and GMOS/Gemini observations. We combine our sample with 12 galaxies at
z
∼ 0.5–2.5 from the literature. We find that the resolved velocity dispersion is systematically lower by a factor 2.45 ± 0.38 for the molecular gas compared to the ionized gas, after correcting for thermal broadening. This offset is constant within the galaxy disks and indicates the coexistence of a thin molecular gas disk and a thick ionized one. This result has a direct impact on the Toomre
Q
and pressure derived in galaxies. We obtain pressures ∼0.22 dex lower on average when using the molecular gas velocity dispersion,
σ
0,mol
. We find that
σ
0,mol
increases with gas fraction and star formation rate. We also obtain an increase with redshift and show that the EAGLE and FIRE simulations overall overestimate
σ
0,mol
at high redshift. Our results suggest that efforts to compare the kinematics of gas using ionized gas as a proxy for the total gas may overestimate the velocity dispersion by a significant amount in galaxies at the peak of cosmic star formation. When using the molecular gas as a tracer, our sample is not consistent with predictions from star formation models with constant efficiency, even when including transport as a source of turbulence. Feedback models with variable star formation efficiency,
ϵ
ff
, and/or feedback efficiency,
p
*
/
m
*
, better predict our observations.
Abstract
We analyse the velocity dispersion properties of 472 z ∼ 0.9 star-forming galaxies observed as part of the KMOS Redshift One Spectroscopic Survey (KROSS). The majority of this sample is ...rotationally dominated (83 ± 5 per cent with vC/σ0 > 1) but also dynamically hot and highly turbulent. After correcting for beam smearing effects, the median intrinsic velocity dispersion for the final sample is σ0 = 43.2 ± 0.8 km s−1 with a rotational velocity to dispersion ratio of vC/σ0 = 2.6 ± 0.1. To explore the relationship between velocity dispersion, stellar mass, star formation rate, and redshift, we combine KROSS with data from the SAMI survey (z ∼ 0.05) and an intermediate redshift MUSE sample (z ∼ 0.5). Whilst there is, at most, a weak trend between velocity dispersion and stellar mass, at fixed mass there is a strong increase with redshift. At all redshifts, galaxies appear to follow the same weak trend of increasing velocity dispersion with star formation rate. Our results are consistent with an evolution of galaxy dynamics driven by discs that are more gas rich, and increasingly gravitationally unstable, as a function of increasing redshift. Finally, we test two analytic models that predict turbulence is driven by either gravitational instabilities or stellar feedback. Both provide an adequate description of the data, and further observations are required to rule out either model.
In this paper we compare the molecular gas depletion times and midplane hydrostatic pressure in turbulent, star-forming disk galaxies to internal properties of these galaxies. For this analysis we ...use 17 galaxies from the DYNAMO sample of nearby (z ∼ 0.1) turbulent disks. We find a strong correlation, such that galaxies with lower molecular gas depletion time (tdep) have higher gas velocity dispersion ( ). Within the scatter of our data, our observations are consistent with the prediction that made in theories of feedback-regulated star formation. We also show a strong, single power-law correlation between midplane pressure (P) and star formation rate surface density ( SFR), which extends for 6 orders of magnitude in pressure. Disk galaxies with lower pressure are found to be roughly in agreement with theoretical predictions. However, in galaxies with high pressure we find P/ SFR values that are significantly larger than theoretical predictions. Our observations could be explained with any of the following: (1) the correlation of SFR−P is significantly sublinear; (2) the momentum injected from star formation feedback (p*/m*) is not a single, universal value; or (3) alternate sources of pressure support are important in gas-rich disk galaxies. Finally, using published survey results, we find that our results are consistent with the cosmic evolution of tdep(z) and (z). Our interpretation of these results is that the cosmic evolution of tdep may be regulated not just by the supply of gas but also by the internal regulation of star formation via feedback.
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