We make use of a semi-analytical model of galaxy formation to investigate the origin of the observed correlation between alpha /Fe abundance ratios and stellar mass in elliptical galaxies. We ...implement a new galaxy-wide stellar initial mass function (IMF; top-heavy integrated galaxy initial mass function, TH-IGIMF) in the semi-analytic model SAG (acronym for semi-analytic galaxies) and evaluate its impact on the chemical evolution of galaxies. The star formation rate (SFR) dependence of the slope of the TH-IGIMF is found to be key to reproducing the correct alpha /Fe-stellar mass relation. Massive galaxies reach higher alpha /Fe abundance ratios because they are characterized by more top-heavy IMFs as a result of their higher SFR. As a consequence of our analysis, the value of the minimum embedded star cluster mass and of the slope of the embedded cluster mass function, which are free parameters involved in the TH-IGIMF theory, are found to be as low as 5 and 2 M..., respectively. A mild downsizing trend is present for galaxies generated assuming either a universal IMF or a variable TH-IGIMF. We find that, regardless of galaxy mass, older galaxies (with formation redshifts ...2) are formed in shorter time-scales (...2 Gyr), thus achieving larger alpha /Fe values. Hence, the time-scale of galaxy formation alone cannot explain the slope of the alpha /Fe-galaxy mass relation, but is responsible for the big dispersion of alpha /Fe abundance ratios at fixed stellar mass. We further test the hypothesis of a TH-IGIMF in elliptical galaxies by looking into mass-to-light ratios, and luminosity functions. Models with a TH-IGIMF are also favoured by these constraints. In particular, mass-to-light ratios agree with observed values for massive galaxies while being overpredicted for less massive ones; this overprediction is present regardless of the IMF considered. (ProQuest: ... denotes formulae/symbols omitted.)
Abstract
We introduce the Automatic Learning for the Rapid Classification of Events (ALeRCE) broker, an astronomical alert broker designed to provide a rapid and self-consistent classification of ...large etendue telescope alert streams, such as that provided by the Zwicky Transient Facility (ZTF) and, in the future, the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST). ALeRCE is a Chilean-led broker run by an interdisciplinary team of astronomers and engineers working to become intermediaries between survey and follow-up facilities. ALeRCE uses a pipeline that includes the real-time ingestion, aggregation, cross-matching, machine-learning (ML) classification, and visualization of the ZTF alert stream. We use two classifiers: a stamp-based classifier, designed for rapid classification, and a light curve–based classifier, which uses the multiband flux evolution to achieve a more refined classification. We describe in detail our pipeline, data products, tools, and services, which are made public for the community (see
https://alerce.science
). Since we began operating our real-time ML classification of the ZTF alert stream in early 2019, we have grown a large community of active users around the globe. We describe our results to date, including the real-time processing of 1.5 × 10
8
alerts, the stamp classification of 3.4 × 10
7
objects, the light-curve classification of 1.1 × 10
6
objects, the report of 6162 supernova candidates, and different experiments using LSST-like alert streams. Finally, we discuss the challenges ahead in going from a single stream of alerts such as ZTF to a multistream ecosystem dominated by LSST.
Context. Submillimetre galaxies (SMGs) represent an important source population in the origin and cosmic evolution of the most massive galaxies. Hence, it is imperative to place firm constraints on ...the fundamental physical properties of large samples of SMGs. Aims. We determine the physical properties of a sample of SMGs in the COSMOS field that were pre-selected at the observed-frame wavelength of λobs = 1.1 mm, and followed up at λobs = 1.3 mm with the Atacama Large Millimetre/submillimetre Array (ALMA). Methods. We used the MAGPHYS model package to fit the panchromatic (ultraviolet to radio) spectral energy distributions (SEDs) of 124 of the target SMGs, which lie at a median redshift of z = 2.30 (19.4% are spectroscopically confirmed). The SED analysis was complemented by estimating the gas masses of the SMGs by using the λobs = 1.3 mm dust emission as a tracer of the molecular gas component. Results. The sample median and 16th–84th percentile ranges of the stellar masses, obscured star formation rates, dust temperatures, and dust and gas masses were derived to be log(M⋆/M⊙) = 11.09+0.41-0.53, SFR = 402+661-233 M⊙ yr-1, Tdust = 39.7+9.7-7.4 K, log(Mdust/M⊙) = 9.01+0.20-0.31, and log(Mgas/M⊙ = 11.34+0.20-0.23, respectively. The Mdust/M⋆ ratio was found to decrease as a function of redshift, while the Mgas/Mdust ratio shows the opposite, positive correlation with redshift. The derived median gas-to-dust ratio of 120+73-30 agrees well with the canonical expectation. The gas fraction (Mgas/ (Mgas + M⋆)) was found to range from 0.10 to 0.98 with a median of 0.62+0.27-0.23. We found that 57.3% of our SMGs populate the main sequence (MS) of star-forming galaxies, while 41.9% of the sources lie above the MS by a factor of greater than three (one source lies below the MS). These super-MS objects, or starbursts, are preferentially found at z ≳ 3, which likely reflects the sensitivity limit of our source selection. We estimated that the median gas consumption timescale for our SMGs is ~535 Myr, and the super-MS sources appear to consume their gas reservoir faster than their MS counterparts. We found no obvious stellar mass–size correlations for our SMGs, where the sizes were measured in the observed-frame 3 GHz radio emission and rest-frame UV. However, the largest 3 GHz radio sizes are found among the MS sources. Those SMGs that appear irregular in the rest-frame UV are predominantly starbursts, while the MS SMGs are mostly disk-like. Conclusions. The physical parameter distributions of our SMGs and those of the equally bright, 870 μm selected SMGs in the ECDFS field (the so-called ALESS SMGs) are unlikely to be drawn from common parent distributions. This might reflect the difference in the pre-selection wavelength. Albeit being partly a selection bias, the abrupt jump in specific SFR and the offset from the MS of our SMGs at z ≳ 3 might also reflect a more efficient accretion from the cosmic gas streams, higher incidence of gas-rich major mergers, or higher star formation efficiency at z ≳ 3. We found a rather flat average trend between the SFR and dust mass, but a positive SFR−Mgas correlation. However, to address the questions of which star formation law(s) our SMGs follow, and how they compare with the Kennicutt-Schmidt law, the dust-emitting sizes of our sources need to be measured. Nonetheless, the larger radio-emitting sizes of the MS SMGs compared to starbursts is a likely indication of their more widespread, less intense star formation activity. The irregular rest-frame UV morphologies of the starburst SMGs are likely to echo their merger nature. The current stellar mass content of the studied SMGs is very high, so they must quench to form the so-called red-and-dead massive ellipticals. Our results suggest that the transition from high-z SMGs to local ellipticals via compact, quiescent galaxies (cQGs) at z ~ 2 might not be universal, and the latter population might also descend from the so-called blue nuggets. However, z ≳ 4 SMGs could be the progenitors of higher redshift, z ≳ 3 cQGs, while our results are also consistent with the possibility that ultra-massive early-type galaxies found at 1.2 ≲ z ≲ 2 experienced an SMG phase at z ≤ 3.
Abstract
The classic classification scheme for active galactic nuclei (AGNs) was recently challenged by the discovery of the so-called changing-state (changing-look) AGNs. The physical mechanism ...behind this phenomenon is still a matter of open debate and the samples are too small and of serendipitous nature to provide robust answers. In order to tackle this problem, we need to design methods that are able to detect AGNs right in the act of changing state. Here we present an anomaly-detection technique designed to identify AGN light curves with anomalous behaviors in massive data sets. The main aim of this technique is to identify CSAGN at different stages of the transition, but it can also be used for more general purposes, such as cleaning massive data sets for AGN variability analyses. We used light curves from the Zwicky Transient Facility data release 5 (ZTF DR5), containing a sample of 230,451 AGNs of different classes. The ZTF DR5 light curves were modeled with a Variational Recurrent Autoencoder (VRAE) architecture, that allowed us to obtain a set of attributes from the VRAE latent space that describes the general behavior of our sample. These attributes were then used as features for an Isolation Forest (IF) algorithm that is an anomaly detector for a “one class” kind of problem. We used the VRAE reconstruction errors and the IF anomaly score to select a sample of 8809 anomalies. These anomalies are dominated by bogus candidates, but we were able to identify 75 promising CSAGN candidates.
Abstract
We present a set of multiwavelength mosaics and photometric catalogs in the Atacama Large Millimeter/submillimeter Array (ALMA) lensing cluster survey fields. The catalogs were built by the ...reprocessing of archival data from the Complete Hubble Archive for Galaxy Evolution compilation, taken by the Hubble Space Telescope (HST) in the Reionization Lensing Cluster Survey, Cluster Lensing And Supernova survey with Hubble, and Hubble Frontier Fields. Additionally, we have reconstructed the Spitzer Infrared Array Camera 3.6 and 4.5
μ
m mosaics, by utilizing all the available archival IPAC Infrared Science Archive/Spitzer Heritage Archive exposures. To alleviate the effect of blending in such a crowded region, we have modeled the Spitzer photometry by convolving the HST detection image with the Spitzer point-spread function using the novel
golfir
software. The final catalogs contain 218,000 sources, covering a combined area of 690 arcmin
2
, a factor of ∼2 improvement over the currently existing photometry. A large number of detected sources is a result of reprocessing of all available and sometimes deeper exposures, in conjunction with a combined optical–near-IR detection strategy. These data will serve as an important tool in aiding the search of the submillimeter galaxies in future ALMA surveys, as well as follow-ups of the HST dark and high-
z
sources with JWST. Coupled with the available HST photometry, the addition of the 3.6 and 4.5
μ
m bands will allow us to place a better constraint on the photometric redshifts and stellar masses of these objects, thus giving us an opportunity to identify high-redshift candidates for spectroscopic follow-ups and to answer the important questions regarding the Epoch of Reionization and formation of the first galaxies. The mosaics, photometric catalogs, and the best-fit physical properties are publicly available at
https://github.com/dawn-cph/alcs-clusters
.
Abstract We report an analysis of a sample of 186 spectroscopically confirmed Type II supernova (SN) light curves (LCs) obtained from a combination of Zwicky Transient Facility (ZTF) and Asteroid ...Terrestrial-impact Last Alert System observations. We implement a method to infer physical parameters from these LCs using hydrodynamic models that take into account the progenitor mass, the explosion energy, and the presence of circumstellar matter (CSM). The CSM is modeled via the mass-loss rate, wind acceleration at the surface of the progenitor star with a β velocity law, and the CSM radius. We also infer the time of explosion, attenuation ( A V ), and the redshift for each SN. Our results favor low-mass progenitor stars ( M ZAMS < 14 M ⊙ ) with a dense CSM ( M ̇ > 10 −3 M ⊙ yr −1 , CSM radius ∼ 10 15 cm, and β > 2). Additionally, we find that the redshifts inferred from the SN LCs are significantly more accurate than those inferred using the host galaxy photometric redshift, suggesting that this method could be used to infer more accurate host galaxy redshifts from large samples of Type II SNe in the LSST era. Lastly, we compare our results with similar works from the literature.
ABSTRACT
PBC J2333.9−2343 is a giant radio galaxy at z = 0.047 with a bright central core associated to a blazar nucleus. If the nuclear blazar jet is a new phase of the jet activity, then the small ...orientation angle suggests a dramatic change of the jet direction. We present observations obtained between 2018 September and 2019 January (cadence larger than three days) with Effeslberg, SMARTS-1.3m, ZTF, ATLAS, Swift, and Fermi-LAT, and between 2019 April and 2019 July (daily cadence) with SMARTS-1.3 m and ATLAS. Large (>2 ×) flux increases are observed on time-scales shorter than a month, which are interpreted as flaring events. The cross correlation between the SMARTS-1.3 m monitoring in the NIR and optical shows that these data do not show significant time lag within the measured errors. A comparison of the optical variability properties between non-blazars and blazars AGN shows that PBC J2333.9−2343 has properties more comparable to the latter. The SED of the nucleus shows two peaks, that were fitted with a one-zone leptonic model. Our data and modelling show that the high energy peak is dominated by External Compton from the dusty torus with mild contribution from Inverse Compton from the jet. The derived jet angle of 3 deg is also typical of a blazar. Therefore, we confirm the presence of a blazar-like core in the centre of this giant radio galaxy, likely a Flat Spectrum Radio Quasar with peculiar properties.
The ALMA Frontier Fields Survey Muñoz Arancibia, A. M.; González-López, J.; Ibar, E. ...
Astronomy and astrophysics (Berlin),
07/2023, Letnik:
675
Journal Article
Recenzirano
Odprti dostop
Context.
Probing the faint end of the number counts at millimeter wavelengths is important in order to identify the origin of the extragalactic background light in this regime. Aided by strong ...gravitational lensing, ALMA observations toward massive galaxy clusters have opened a window to probe this origin, allowing us to resolve sub-milliJansky dusty star-forming galaxies.
Aims.
We aim to derive number counts at 1.1 mm down to flux densities fainter than 0.1 mJy based on ALMA observations toward five
Hubble
Frontier Fields (FF) galaxy clusters, following a statistical approach to correct for lensing effects.
Methods.
We created a source catalog that includes ALMA 1.1 mm continuum detections around two new FF galaxy clusters, together with the sources previously detected around three FF galaxy clusters, making a total of 29 detected sources down to a 4.5
σ
significance. ALMA 1.1 mm mosaics used for our source extraction covered the inner ≈2′×2′ FF regions, reached rms depths of ≈55 − 71 μJy beam
−1
, and had synthesized beam sizes from ≈0″.5 − 1″.5 (natural weighting). We derived source intrinsic flux densities using public lensing models. We folded the uncertainties in both magnifications and source redshifts into the number counts through Monte Carlo simulations.
Results.
Using the combination of all cluster fields, we derive cumulative number counts over two orders of magnitude down to ≈0.01 mJy after correction for lensing effects. Cosmic variance estimates are all exceeded by uncertainties in our median combined cumulative counts that come from both our Monte Carlo simulations and Poisson statistics. Our number counts agree at a 1
σ
level with our previous estimates using ALMA observations of the first three FFs, exhibiting a similar flattening at faint flux densities. They are also consistent to 1
σ
with most recent ALMA estimates and galaxy evolution models. However, below ≈0.1 mJy, our cumulative number counts are lower by ≈0.4 dex compared to two deep ALMA studies (namely one that probes several blank fields plus one lensed galaxy cluster, and the initial ALMA Spectroscopic Survey in the
Hubble
Ultra Deep Field, ASPECS-Pilot), while remaining consistent with the ASPECS Large Program (ASPECS-LP) within 1
σ
. Importantly, the flattening found for our cumulative counts at ≲0.1 mJy also extends further to ≈0.01 mJy, that is, ≈0.4 dex fainter than ASPECS-LP, and remains in agreement with extrapolations of their number counts down to this flux limit. We find a median contribution to the extragalactic background light (EBL) of 14
−8
+12
Jy deg
−2
resolved in our demagnified sources down to ≈0.01 mJy, representing 75 − 86% of
Planck
-derived extragalactic EBL estimates at 1.1 mm.
Conclusions.
We estimate cumulative 1.1 mm number counts down to ≈0.01 mJy along the line of sight of five galaxy clusters that benefit from having rich deep multiwavelength data. They bring further support to the flattening of the number counts reported previously by us and ASPECS-LP, which has been interpreted by a recent galaxy evolution model as a measurement of the “knee” of the infrared luminosity function at high redshift. Our estimates of the contribution to the EBL associated with 1.1 mm galaxies in the FFs suggest that we may be resolving most of the EBL at this wavelength down to ≈0.01 mJy.
The ALMA Frontier Fields Survey Laporte, N.; Bauer, F. E.; Troncoso-Iribarren, P. ...
Astronomy and astrophysics (Berlin),
08/2017, Letnik:
604
Journal Article
Abstract
In this work, we present new the Swedish-ESO PI receiver for the Atacama Pathfinder Experiment APEX/SEPIA Band-5 observations targeting the CO (J = 2–1) emission line of 24 Herschel-detected ...galaxies at z = 0.1–0.2. Combining this sample with our recent new Valparaíso ALMA Line Emission Survey (VALES), we investigate the star formation efficiencies SFEs = star formation rate (SFR)/$M_{\rm H_{2}}$ of galaxies at low redshift. We find the SFE of our sample bridges the gap between normal star-forming galaxies and Ultra-Luminous Infrared Galaxies (ULIRGs), which are thought to be triggered by different star formation modes. Considering the SFE΄ as the SFR and the $L^{\prime }_{\rm CO}$ ratio, our data show a continuous and smooth increment as a function of infrared luminosity (or star formation rate) with a scatter about 0.5 dex, instead of a steep jump with a bimodal behaviour. This result is due to the use of a sample with a much larger range of sSFR/sSFRms using LIRGs, with luminosities covering the range between normal and ULIRGs. We conclude that the main parameters controlling the scatter of the SFE in star-forming galaxies are the systematic uncertainty of the αCO conversion factor, the gas fraction, and physical size.
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