In this paper we show an application of the Minimum Spanning Tree (MST) clustering method to the high-energy
γ
-ray sky observed at energies higher than 10 GeV in 6.3 years by the
Fermi
-Large Area ...Telescope. We report the detection of 19 new high-energy
γ
-ray clusters with good selection parameters whose centroid coordinates were found matching the positions of known BL Lac objects in the 5th Edition of the Roma-BZCAT catalogue. A brief summary of the properties of these sources is presented.
We combine results from deep ALMA observations of massive (
M
*
> 10
10
M
⊙
) galaxies at different redshifts to show that the column density of their interstellar medium (ISM) rapidly increases ...toward early cosmic epochs. Our analysis includes objects from the ASPECS and ALPINE large programs, as well as individual observations of
z
∼ 6 quasar hosts. When accounting for non-detections and correcting for selection effects, we find that the median surface density of the ISM of the massive galaxy population evolves as ∼(1 +
z
)
3.3
. This means that the ISM column density toward the nucleus of a
z
> 3 galaxy is typically > 100 times larger than locally, and it may reach values as high as Compton-thick at
z
≳ 6. Remarkably, the median ISM column density is on the same order of what is measured from X-ray observations of large active galactic nucleus (AGN) samples already at
z
≳ 2. We have developed a simple analytic model for the spatial distribution of ISM clouds within galaxies, and estimate the total covering factor toward active nuclei when obscuration by ISM clouds on the host scale is added to that of parsec-scale circumnuclear material (the so-called torus). The model includes clouds with a distribution of sizes, masses, and surface densities, and also allows for an evolution of the characteristic cloud surface density with redshift, Σ
c, *
∝ (1 +
z
)
γ
. We show that, for
γ
= 2, such a model successfully reproduces the increase in the obscured AGN fraction with redshift that is commonly observed in deep X-ray surveys, both when different absorption thresholds and AGN luminosities are considered. Our results suggest that 80–90% of supermassive black holes in the early Universe (
z
> 6 − 8) are hidden to our view, primarily by the ISM in their hosts. We finally discuss the implications of our results and how they can be tested observationally with current and forthcoming facilities (e.g., VLT, E-ELT, ALMA, and JWST) and with next-generation X-ray imaging satellites. By extrapolating the observed X-ray nebulae around local AGN to the environments of supermassive black holes at high redshifts, we find ≲1″ nebulae impose stringent design constraints on the spatial resolution of any future X-ray imaging Great Observatory in the coming decades.
Aims. The standard active galactic nuclei (AGN)-galaxy co-evolutionary scenario predicts a phase of deeply “buried” supermassive black hole growth coexisting with a starburst (SB) before feedback ...phenomena deplete the cold molecular gas reservoir of the galaxy and an optically luminous quasar (QSO) is revealed (called the SB-QSO evolutionary sequence). The aim of this work is to measure the cold gas reservoir of three highly obscured QSOs to test if their gas fraction is similar to that of submillimetre galaxies (SMGs), as expected by some models, and to place these measurements in the context of the SB-QSO framework. Methods. We target CO(1-0) transition in BzK4892, a Compton thick (CT) QSO at z = 2.6, CO(1-0) in BzK8608 and CO(2-1) in CDF153, two highly obscured (NH ≈ 6 × 1023 cm−2) QSOs at z = 2.5 and z = 1.5, respectively. For these targets, we place 3σ upper limits on the CO lines, with L′CO < (1.5 ÷ 2.8)×1010 K km s−1 pc2. We also compare the molecular gas conditions of our targets with those of other systems at z > 1, considering normal star-forming galaxies and SMGs, and unobscured and obscured AGN from the literature. For the AGN samples, we provide an updated and almost complete collection of targets with CO follow-up at z > 1. Results. BzK4892 displays a high star formation efficiency (SFE = LIR/L′CO > 410 L⊙/(K km s−1 pc2 )) and a gas fraction fgas = Mgas/(Mstar + Mgas)< 10%. Less stringent constraints are derived for the other two targets (fgas < 0.5 and SFE > 10 L⊙/(K km s−1 pc2 )). From the comparison with the literature data we found that, on average, i) obscured AGN at z > 1 are associated with higher SFE and lower fgas with respect to normal star-forming galaxies and SMGs; ii) mildly and highly obscured active galaxies have comparable gas fractions; iii) the SFE of CT and obscured AGN are similar to those of unobscured AGN. Conclusions. Within the SB-QSO framework, these findings could be consistent with a scenario where feedback can impact the host galaxy already from the early phases of the SB-QSO evolutionary sequence.
We present Atacama Large Millimeter/submillimeter Array Band 5 observations of a galaxy at z = 1.91, GDS24569, in search of molecular gas in its vicinity via the C i 3P1-3P0 line. GDS24569 is a ...massive ( ), passively evolving galaxy, characterized by compact morphology with an effective radius of ∼0.5 kpc. We apply two blind detection algorithms to the spectral data cubes and find no promising detection in or around GDS24569 out to a projected distance of ∼320 kpc, while a narrow tentative line (4.1 ) is identified at +1200 km s−1 by one of the algorithms. From the nondetection of C i, we place a 3 upper limit on molecular hydrogen mass, ∼ 7.1 × 109 M , which converts to an extremely low gas-to-stellar mass fraction of 5%. We conduct a spectral energy distribution modeling by including optical to far-infrared data and find a considerably high ( ∼ 0.1%) dust-to-stellar mass ratio, i.e., ∼10-100× higher than those of local early-type galaxies. In combination with a previous result of an insufficient number of surrounding satellite galaxies, it is suggested that GDS24569 is unlikely to experience significant size evolution via satellite mergers. We discuss possible physical mechanisms that quenched GDS24569.
Context.
Obscured active galactic nuclei (AGN) represent a significant fraction of the entire AGN population, especially at high redshift (∼70% at
z
= 3 − 5). They are often characterized by the ...presence of large gas and dust reservoirs that are thought to sustain and possibly obscure vigorous star formation processes that make these objects shine at FIR and submillimeter wavelengths. Studying the physical properties of obscured AGN and their host galaxies is crucial to shedding light on the early stages of a massive system lifetime.
Aims.
We aim to investigate the contribution of the interstellar medium (ISM) to the obscuration of quasars in a sample of distant highly star forming galaxies and to unveil their morphological and kinematics properties.
Methods.
We exploit Atacama Large Millimeter/submillimeter Array Cycle 4 observations of the continuum (∼2.1 mm) and high-
J
CO emission of a sample of six X-ray selected, FIR detected galaxies hosting an obscured AGN at
z
spec
> 2.5 in the 7 Ms
Chandra
Deep Field-South. We measured the masses and sizes of the dust and molecular gas by fitting the images, visibilities, and spectra, and we derived the gas density and column density on the basis of a uniform sphere geometry. Finally, we compared the measured column densities with those derived from the
Chandra
X-ray spectra.
Results.
We detected both the continuum and line emission for three sources for which we measured both the flux density and size. For the undetected sources, we derived an upper limit on the flux density from the root mean square of the images. We found that the detected galaxies are rich in gas and dust (molecular gas mass in the range < 0.5–2.7 × 10
10
M
⊙
for
α
CO
= 0.8 and up to ∼2 × 10
11
M
⊙
for
α
CO
= 6.5, and dust mass < 0.9–4.9 × 10
8
M
⊙
) and generally compact (gas major axis 2.1–3.0 kpc, dust major axis 1.4–2.7 kpc). The column densities associated with the ISM are on the order of 10
23 − 24
cm
−2
, which is comparable with those derived from the X-ray spectra. For the detected sources we also derived dynamical masses in the range 0.8–3.7 × 10
10
M
⊙
.
Conclusions.
We conclude that the ISM of high redshift galaxies can substantially contribute to nuclear obscuration up to the Compton-thick (> 10
24
cm
−2
) regime. In addition, we found that all the detected sources show a velocity gradient reminding one rotating system, even though two of them show peculiar features in their morphology that can be associated with a chaotic, possibly merging, structure.
We report the discovery of a galaxy overdensity around a Compton-thick Fanaroff–Riley type II (FRII) radio galaxy at z = 1.7 in the deep multiband survey around the z = 6.3 quasi-stellar object (QSO) ...SDSS J1030+0524. Based on a 6 h VLT/MUSE and on a 4 h LBT/LUCI observation, we identify at least eight galaxy members in this structure with spectroscopic redshift z = 1.687 − 1.699, including the FRII galaxy at z = 1.699. Most members are distributed within 400 kpc from the FRII core. Nonetheless, the whole structure is likely much more extended, as one of the members was serendipitously found at ∼800 kpc projected separation. The classic radio structure of the FRII itself extends for ∼600 kpc across the sky. Most of the identified overdensity members are blue, compact galaxies that are actively forming stars at rates of ∼8–60 M⊙ yr−1. For the brightest of them, a half-light radius of 2.2 ± 0.8 kpc at 8000 Å rest-frame was determined based on adaptive optics-assisted observations with LBT/SOUL in the Ks band. We do not observe any strong galaxy morphological segregation or concentration around the FRII core. This suggests that the structure is far from being virialized and likely constitutes the progenitor of a local massive galaxy group or cluster caught in its main assembly phase. Based on a 500 ks Chandra ACIS-I observation, we found that the FRII nucleus hosts a luminous QSO (L2 − 10 keV = 1.3 × 1044 erg s−1, intrinsic and rest-frame) that is obscured by Compton-thick absorption (NH = 1.5 ± 0.6 × 1024 cm−2). Under standard bolometric corrections, the total measured radiative power (Lrad ∼ 4 × 1045 erg s−1) is similar to the jet kinetic power that we estimated from radio observations at 150 MHz (Pkin = 6.3 × 1045 erg s−1), in agreement with what is observed in powerful jetted AGN. Our Chandra observation is the deepest so far for a distant FRII within a galaxy overdensity. It revealed significant diffuse X-ray emission within the region that is covered by the overdensity. In particular, X-ray emission extending for ∼240 kpc is found around the eastern lobe of the FRII. Four out of the six MUSE star-forming galaxies in the overdensity are distributed in an arc-like shape at the edge of this diffuse X-ray emission. These objects are concentrated within 200 kpc in the plane of the sky and within 450 kpc in radial separation. Three of them are even more concentrated and fall within 60 kpc in both transverse and radial distance. The probability of observing four out of the six z = 1.7 sources by chance at the edge of the diffuse emission is negligible. In addition, these four galaxies have the highest specific star formation rates of the MUSE galaxies in the overdensity and lie above the main sequence of field galaxies of equal stellar mass at z = 1.7. We propose that the diffuse X-rays originate from an expanding bubble of gas that is shock heated by the FRII jet, and that star formation is promoted by the compression of the cold interstellar medium of the galaxies around the bubble, which may be remarkable evidence of positive AGN feedback on cosmological scales. We emphasize that our conclusions about the feedback are robust because even assuming that the diffuse X-ray emission arises from inverse Compton scattering of photons of the cosmic microwave background by the relativistic electrons in the radio lobe, star formation may be promoted by the nonthermal pressure of the expanding lobe.
Based on ALMA Band 3 observations of the CO(2→1) line transition, we report the discovery of three new gas-rich (
M
H
2
∼ 1.5 − 4.8 × 10
10
M
⊙
) galaxies in an overdense region at
z
= 1.7 that ...already contains eight spectroscopically confirmed members. This leads to a total of 11 confirmed overdensity members within a projected distance of ∼1.15 Mpc and in a redshift range of Δ
z
= 0.012. Under simple assumptions, we estimate that the system has a total mass of ≥3 − 6 × 10
13
M
⊙
, and show that it will likely evolve into a ≳10
14
M
⊙
cluster at
z
= 0. The overdensity includes a powerful Compton-thick Fanaroff-Riley type II (FRII) radio galaxy, around which we discovered a large molecular gas reservoir (
M
H
2
∼ 2 × 10
11
M
⊙
). We fit the FRII resolved CO emission with a 2D Gaussian model with a major (minor) axis of ∼27 (∼17) kpc, which is a factor of ∼3 larger than the optical rest-frame emission. Under the assumption of a simple edge-on disk morphology, we find that the galaxy interstellar medium produces a column density toward the nucleus of ∼5.5 × 10
23
cm
−2
. A dense interstellar medium like this may then contribute significantly to the total nuclear obscuration measured in the X-rays (
N
H, X
∼ 1.5 × 10
24
cm
−2
) in addition to a small, paresec-scale absorber around the central engine. The velocity map of this source unveils a rotational motion of the gas that is perpendicular to the radio jets. All ALMA sources have a dust-reddened counterpart in deep
Hubble
Space Telescope images (bands
i
,
z
,
H
), while we do not detect any molecular gas reservoir around the known UV-bright, star-forming members discovered by MUSE. This highlights the capability of ALMA of tracing gas-rich members of the overdensity. For the MUSE sources, we derive 3
σ
upper limits to the molecular gas mass of
M
H
2
≤ 2.8 − 4.8 × 10
10
M
⊙
. We derive star formation rates in the range ∼5 − 100
M
⊙
yr
−1
for the three new ALMA sources. The FRII is located at the center of the projected spatial distribution of the structure members, and its velocity offset from the peak of the redshift distribution is well within the velocity dispersion of the structure. All this, coupled with the large amount of gas around the FRII, its stellar mass of ∼3 × 10
11
M
⊙
, star formation rate of ∼200 − 600
M
⊙
yr
−1
, and powerful radio-to-X-ray emission, suggests that this source is the likely progenitor of the future brightest cluster galaxy.
Bolstered 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.
We present deep
L
-Band observations of the equatorial field centered on the
z
= 6.3 Sloan Digital Sky Survey (SDSS) quasar (QSO). This field is rich of multiwavelength photometry and spectroscopy ...data, making it an ideal laboratory for galaxy evolution studies. Our observations reach a 1
σ
sensitivity of ~2.5 µJy at the center of the field. We extracted a catalog of 1489 radio sources down to a flux density of ~12.5 µJy (5
σ
) over a field of view of ~ 30′ diameter. We derived the source counts accounting for catalog reliability and completeness, and compared them with others available in the literature. Our source counts are among the deepest available so far, and, overall, are consistent with recent counts’ determinations and models. They show a slight excess at flux densities ~50 µJy, possibly associated with the presence of known overdensities in the field. We detected for the first time in the radio band the SDSS J1030+0524 QSO (26 ± 5 µJy, 8
σ
significance level). For this object, we derived an optical radio loudness
R
O
= 0.62±0.12, which makes it the most radio quiet among active galactic nuclei (AGN) discovered so far at z ≳ 6 and detected at radio wavelengths. We unveiled extended diffuse radio emission associated with the lobes of a bright Fanaroff-Riley type II (FRII) radio galaxy located close to the center of the J1030 field, which is likely to become the future brightest cluster galaxy of a protocluster at z = 1.7. The lobes’ complex morphology, coupled with the presence of X-ray diffuse emission detected around the FRII galaxy lobes, may point toward an interaction between the radio jets and the external medium. We also investigated the relation between radio and X-ray luminosity for a sample of 243 X-ray-selected objects obtained from 500 ks
Chandra
observations of the same field, and spanning a wide redshift range (0 ≲
z
≲ 3). Focused on sources with a spectroscopic redshift and classification, we found that sources hosted by early-type galaxies and AGN follow log(
L
R
)/log(
L
X
) linear correlations with slopes of ~0.6 and ~0.8, respectively. This is interpreted as a likely signature of different efficiency in the accretion process. Finally, we found that most of these sources (≳87%) show a radio-to-X-ray radio loudness
R
X
≲ −3.5, classifying these objects as radio quiet.
Aims. Measurements of the size of dust continuum emission are an important tool for constraining the spatial extent of star formation, and hence the buildup of stellar mass. Compact dust emission has ...generally been observed at cosmic noon ( z ∼ 2 − 3). However, at earlier epochs, toward the end of the reionization ( z ∼ 4 − 6), only the sizes of a handful of infrared (IR) bright galaxies have been measured. In this work, we derive the dust emission sizes of main-sequence (MS) galaxies at z ∼ 5 from the ALPINE survey. Methods. We measured the dust effective radius, r e, FIR , in the uv -plane in Band 7 of ALMA for seven ALPINE galaxies with resolved emission and we compared it with rest-frame ultraviolet (UV) and CII158 μm measurements. We studied the r e, FIR − L IR scaling relation by considering our dust size measurements and all the data in the literature at z ∼ 4 − 6. Finally, we compared our size measurements with predictions from simulations. Results. The dust emission in the selected ALPINE galaxies is rather extended ( r e, FIR ∼ 1.5 − 3 kpc), similar to CII158 μm but a factor of ∼2 larger than the rest-frame UV emission. Putting together all the measurements at z ∼ 5, spanning two decades in luminosity from L IR ∼ 10 11 L ⊙ to L IR ∼ 10 13 L ⊙ , the data highlight a steeply increasing trend of the r e, FIR − L IR relation at L IR < 10 12 L ⊙ , followed by a downturn and a decreasing trend at brighter luminosities. Finally, simulations that extend up to the stellar masses of the ALPINE galaxies considered in the present work predict a subset of galaxies (∼25% at 10 10 M ⊙ < M ⋆ < 10 11 M ⊙ ) with sizes as large as those measured.
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