22 research outputs found
ALMA resolves the first strongly-lensed Optical/NIR-dark galaxy
No full textWe present high-resolution (arcsec) ALMA observations of the
strongly-lensed galaxy HATLASJ113526.2-01460 at redshift discovered
in the Gama 12 field of the Herschel-ATLAS survey. The
gravitationally lensed system is remarkably peculiar in that neither the
background source nor the foreground lens show a clearly detected optical/NIR
emission. We perform accurate lens modeling and source morphology
reconstruction in three different (sub-)mm continuum bands, and in the C[II]
and CO(8-7) spectral lines. The modeling indicates a foreground lensing (likely
elliptical) galaxy with mass at , while
the source (sub-)mm continuum and line emissions are amplified by factors
. We estimate extremely compact sizes kpc for the
star-forming region and kpc for the gas component, with no clear
evidence of rotation or of ongoing merging events. We perform broadband
SED-fitting and retrieve the intrinsic de-magnified physical properties of the
source, which is found to feature a very high star-formation rate
yr, that given the compact sizes is on the verge
of the Eddington limit for starbursts; the radio luminosity at 6 cm from
available EVLA observations is consistent with the star-formation activity. The
galaxy is found to be extremely rich in gas and dust
. The stellar content places
the source well above the main sequence of starforming galaxies, indicating
that the starburst is rather young with estimated age yr. Our
results indicate that the overall properties of HATLASJ113526.2-01460 are
consistently explained by in-situ galaxy formation and evolution scenarios.Comment: 17 Pages, 12 Figures, 7 Tables. Submitted to Ap
The far-infrared/radio correlation for a sample of strongly lensed dusty star-forming galaxies detected by Herschel
No full textWe investigate the radio/far-infrared (FIR) correlation for a sample of 28 bright high-redshift (1 z 4) star-forming galaxies selected in the FIR from the Herschel -ATLAS fields as candidates to be strongly gravitationally lensed. The radio information comes either from high sensitivity dedicated Australia Telescope Compact Array observations at 2.1 GHz or from cross-matches with the FIRST surv e y at 1.4 GHz. By taking advantage of source brightness possibly enhanced by lensing magnification, we identify a weak evolution with redshift out to z 4 of the FIR-to-radio luminosity ratio q FIR . We also find that the q FIR parameter as a function of the radio power L 1 . 4 GHz displays a clear decreasing trend, similarly to what is observed for optically/radio- selected lensed quasars found in literature, yet co v ering a complementary region in the q FIR –L 1 . 4 GHz diagram. We interpret such a behaviour in the framework of an in situ galaxy formation scenario, as a result of the transition from an early dust-obscured star-forming phase (mainly pinpointed by our FIR selection) to a late radio-loud quasar phase (preferentially sampled by the optical/radio selection)
A
No full textAims. We leverage the largest available Atacama Large Millimeter/submillimeter Array (ALMA) survey from the archive (A3COSMOS) to study infrared luminosity function and dust-obscured star formation rate density of (sub)millimeter galaxies from z = 0.5 − 6.
Methods. The A3COSMOS survey utilizes all publicly available ALMA data in the COSMOS field and therefore has inhomogeneous coverage in terms of observing wavelength and depth. In order to derive the luminosity functions and star formation rate densities, we applied a newly developed method that corrects the statistics of an inhomogeneously sampled survey of individual pointings to those representing an unbiased blind survey.
Results. We find our sample to mostly consist of massive (M⋆ ∼ 1010 − 1012 M⊙) IR-bright (L* ∼ 1011 − 1013.5 L⊙) highly star-forming (SFR ∼100 − 1000 M⊙
yr−1) galaxies. We find an evolutionary trend in the typical density (Φ*) and luminosity (L*) of the galaxy population that respectively decreases and increases with redshift. Our infrared luminosity function (LF) is in agreement with previous literature results, and we were able to extend the constraints on the knee and bright end of the LF to high redshift (z > 3) by using the Herschel data. Finally, we obtained the star formation rate density up to z ∼ 6 by integrating the IR LF, finding a broad peak from z ∼ 1 to z ∼ 3 and a decline toward higher redshifts, in agreement with recent IR/millimeter-based studies, within the uncertainties. These results imply the presence of larger quantities of dust than what is expected based on optical/UV studies
Illuminating the Dark Side of Cosmic Star Formation. II. A Second Date with RS-NIRdark Galaxies in COSMOS
No full textAbout 12 billion years ago, the Universe was first experiencing light again after the dark ages, and galaxies filled
the environment with stars, metals, and dust. How efficient was this process? How fast did these primordial
galaxies form stars and dust? We can answer these questions by tracing the star formation rate density (SFRD)
back to its widely unknown high-redshift tail, traditionally observed in the near-infrared (NIR), optical, and UV
bands. Thus, objects with a large amount of dust were missing. We aim to fill this knowledge gap by studying
radio-selected NIR-dark (RS-NIRdark) sources, i.e., sources not having a counterpart at UV-to-NIR wavelengths.
We widen the sample of Talia et al. from 197 to 272 objects in the Cosmic Evolution Survey (COSMOS) field,
including also photometrically contaminated sources, which were previously excluded. Another important step
forward consists in the visual inspection of each source in the bands from u* to MIPS 24 μm. According to their
“environment” in the different bands, we are able to highlight different cases of study and calibrate an appropriate
photometric procedure for the objects affected by confusion issues. We estimate that the contribution of RSNIRdark
sources to the cosmic SFRD at 3 < z < 5 is ∼10%–25% of that based on UV-selected galaxies
GalaPy: A highly optimised C++/Python spectral modelling tool for galaxies: I. Library presentation and photometric fitting
No full textBolstered by upcoming data from new-generation observational campaigns, we are about to enter a new era in the study of how galaxies form and evolve. The unprecedented quantity of data that will be collected from distances that have only marginally been grasped up to now will require analytical tools designed to target the specific physical peculiarities of the observed sources and handle extremely large datasets. One powerful method to investigate the complex astrophysical processes that govern the properties of galaxies is to model their observed spectral energy distributions (SEDs) at different stages of evolution and times throughout the history of the Universe. To address these challenges, we have developed GalaPy, a new library for modelling and fitting SEDs of galaxies from the X-ray to the radio band, as well as the evolution of their components and dust attenuation and reradiation. On the physical side, GalaPy incorporates both empirical and physically motivated star formation histories (SFHs), state-of-the-art single stellar population synthesis libraries, a two-component dust model for attenuation, an age-dependent energy conservation algorithm to compute dust reradiation, and additional sources of stellar continuum such as synchrotron, nebular and free-free emission, as well as X-ray radiation from low-and high-mass binary stars. On the computational side, GalaPy implements a hybrid approach that combines the high performance of compiled C++ with the user-friendly flexibility of Python. Also, it exploits an object-oriented design via advanced programming techniques. GalaPy is the fastest SED-generation tool of its kind, with a peak performance of almost 1000 SEDs per second. The models are generated on the fly without relying on templates, thus minimising memory consumption. It exploits a fully Bayesian parameter space sampling, which allows for the inference of parameter posteriors and thereby facilitates the study of the correlations between the free parameters and the other physical quantities that can be derived from modelling. The application programming interface (API) and functions of GalaPy are under continuous development, with planned extensions in the near future. In this first work, we introduce the project and showcase the photometric SED fitting tools already available to users. GalaPy is available on the Python Package Index (PyPI) and comes with extensive online documentation and tutorials
Illuminating the Dark Side of Cosmic Star Formation. III. Building the Largest Homogeneous Sample of Radio-selected Dusty Star-forming Galaxies in COSMOS with PhoEBO
No full textan optical/near-IR, hereafter NIR, counterpart) dusty star-forming galaxies (DSFGs). Although extremely
promising for their likely contribution to the cosmic star formation rate density (SFRD) and for their possible role
in the evolution of the first massive and passive galaxies around z ∼ 3, the difficulty in selecting statistically
significant samples of dark DSFGs is limiting their scientific potentialities. This work presents the first
panchromatic study of a sample of 263 radio-selected NIR-dark (RS-NIRdark) galaxies discovered in the
COSMOS field following the procedure by Talia et al. These sources are selected as radio-bright galaxies
(S3 GHz > 12.65 μJy) with no counterpart in the NIR-selected COSMOS2020 catalog (Ks 25.5 mag). For these
sources, we build a new photometric catalog including accurate photometry from the optical to the radio obtained
with a new deblending pipeline (Photometry Extractor for Blended Objects, or PHOEBO). We employ this catalog
to estimate the photo-zs and the physical properties of the galaxies through an spectral energy distribution-fitting
procedure performed with two different codes (MAGPHYS and CIGALE). Finally, we estimate the active galactic
nucleus contamination in our sample by performing a series of complementary tests. The high values of the median
extinction (Av ∼ 4) and star formation rate (SFR ∼ 500Me yr−1) confirm the likely DSFG nature of the RSNIRdark
galaxies. The median photo-z (z ∼ 3) and the presence of a significant tail of high-z candidates (z > 4.5)
suggest that these sources are important contributors to the cosmic SFRD and the evolutionary path of galaxies at
high redshifts
A New Estimate of the Cosmic Star Formation Density from a Radio-selected Sample, and the Contribution of H-dark Galaxies at z ≥ 3
No full textThe star formation rate density (SFRD) history of the universe is well constrained up to redshift z ∼2. At earlier cosmic epochs, the picture has been largely inferred from UV-selected galaxies (e.g., Lyman-break galaxies; LBGs). However, the inferred star formation rates of LBGs strongly depend on the assumed dust extinction correction, which is not well constrained at high z, while observations in the radio domain are not affected by this issue. In this work we measure the SFRD from a 1.4 GHz selected sample of ∼600 galaxies in the GOODS-N field up to redshift ∼3.5. We take into account the contribution of active galactic nuclei from the infrared-radio correlation. We measure the radio luminosity function, fitted with a modified Schechter function, and derive the SFRD. The cosmic SFRD shows an increase up to z ∼2 and then an almost flat plateau up to z ∼3.5. Our SFRD is in agreement with those from other far-IR/radio surveys and a factor 2 higher than those from LBG samples. We also estimate that galaxies lacking a counterpart in the HST/WFC3 H-band (H-dark) make up ∼25% of the φ-integrated SFRD relative to the full sample at z ∼3.2, and up to 58% relative to LBG samples
The Way of Water: ALMA resolves H2O emission lines in a strongly lensed dusty star-forming galaxy at z 3.1
No full textWe report ALMA high-resolution observations of water emission lines
), ,
, in the strongly lensed galaxy
HATLASJ113526.2-01460 at redshift z 3.1. From the lensing-reconstructed
maps of water emission and line profiles, we infer the general physical
properties of the ISM in the molecular clouds where the lines arise. We find
that the water vapor lines , are mainly excited by FIR pumping from dust radiation in a
warm and dense environment, with dust temperatures ranging from 70 K to K, as suggested by the line ratios. The
line instead, is excited by a complex interplay between FIR pumping and
collisional excitation in the dense core of the star-forming region. This
scenario is also supported by the detection of the medium-level excitation of
CO resulting in the line emission CO (J=8-7). Thanks to the unprecedented high
resolution offered by the combination of ALMA capabilities and gravitational
lensing, we discern the different phases of the ISM and locate the hot
molecular clouds into a physical scale of 500 pc. We discuss the
possibility of J1135 hosting an AGN in its accretion phase. Finally, we
determine the relation between the water emission lines and the total IR
luminosity of J1135, as well as the SFR as a function of water emission
intensities, comparing the outcomes to local and high- galactic samples from
the literature.Comment: 22 pages, 10 figures, final version to be published in Astrophysical
Journa
Dark progenitors and massive descendants: A first ALMA perspective of radio-selected near-IR-dark galaxies in the COSMOS field
No full textWe present the first spectroscopic ALMA follow-up for a pilot sample of nine radio-selected near-IR-dark galaxies in the COSMOS field. These sources were initially selected as radio-detected sources (S3GHza> 12.65aμJy) without an optical or near-IR (NIR) counterpart in the COSMOS2015 catalog (Ksa 24.7 mag), and just three of them were subsequently detected in the deeper COSMOS2020. Several studies highlighted that this selection could provide a population of highly dust-obscured, massive, and star-bursting galaxies. With these new ALMA observations, we assess the spectroscopic redshifts of this pilot sample of sources and improve the quality of the physical properties estimated through SED-fitting. Moreover, we measure the quantity of molecular gas inside these galaxies and forecast their potential evolutionary path, finding that the radio-selected NIR-dark galaxies might likely represent a population of high-z progenitors of the massive and passive galaxies that were discovered at za3. Finally, we present some initial constraints on the kinematics of the interstellar medium within the analyzed galaxies, reporting a high fraction (a55%) of double-peaked lines that can be interpreted as the signature of a rotating structure in our targets or as the presence of major mergers in our sample. The results we present here show the scientific potential of (sub)mm observations for this elusive population of galaxies and highlight the potential contribution of these sources to the evolution of the massive and passive galaxies at high z
