arXiv subjects

R. Paladino

Publications and source records attributed to R. Paladino.

At least 37 records · Page 2Linked to original sources

arXiv2022

GASP XXXVII: The Most Extreme Jellyfish Galaxies Compared to Other Disk Galaxies in Clusters, an HI Study

We present the results of a VLA HI imaging survey aimed at understanding why some galaxies develop long extraplanar H$α$ tails, becoming extreme jellyfish galaxies. The observations are centered on five extreme jellyfish galaxies, optically selected from the WINGS and OmegaWINGS surveys and confirmed to have long H$α$ tails through MUSE observations. Each galaxy is located in a different cluster. In the observations there are in total 88 other spiral galaxies within the field of view (40'x40') and observed bandwidth (6500 km s$^{-1}$). We detect 13 of these 88 spirals, plus one uncatalogued spiral, with HI masses ranging from 1 to 7 $\times$ 10${^9}$ M$_{\odot}$. Many of these detections have extended HI disks, two show direct evidence for ram pressure stripping, while others are possibly affected by tidal forces and/or ram-pressure stripping. We stack the 75 non-detected spiral galaxies and find an average HI mass of 1.9 $\times$ 10$^{8}$ M$_{\odot}$, which given their average stellar mass, implies they are very HI deficient. Comparing the extreme jellyfish galaxies to the other disk galaxies, we find that they have a larger stellar mass than almost all disk galaxies and than all HI detected galaxies, they are at smaller projected distance from the cluster center and at higher relative velocity to the cluster mean than all HI detections and most non-detections. We conclude that the high stellar mass allows extreme jellyfish galaxies to fall deeply into the cluster before being stripped and the surrounding ICM pressure gives rise to their spectacular star-forming tails.

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arXiv2021

Multi-Wavelength Study of a Proto-BCG at z = 1.7

In this work we performed a spectral energy distribution (SED) analysis in the optical/infrared band of the host galaxy of a proto-brightest cluster galaxy (BCG, NVSS J103023+052426) in a proto-cluster at z = 1.7. We found that it features a vigorous star formation rate (SFR) of ${\sim}$570 $\mathrm{M_{\odot}}$/yr and a stellar mass of $M_{\ast} \sim 3.7 \times 10^{11}$ $\mathrm{M_{\odot}}$; the high corresponding specific SFR = $1.5 \pm 0.5$ $\mathrm{Gyr^{-1}}$ classifies this object as a starburst galaxy that will deplete its molecular gas reservoir in $\sim$ $3.5 \times 10^8$ yr. Thus, this system represents a rare example of a proto-BCG caught during the short phase of its major stellar mass assembly. Moreover, we investigated the nature of the host galaxy emission at 3.3 mm. We found that it originates from the cold dust in the interstellar medium, even though a minor non-thermal AGN contribution cannot be completely ruled out. Finally, we studied the polarized emission of the lobes at 1.4 GHz. We unveiled a patchy structure where the polarization fraction increases in the regions in which the total intensity shows a bending morphology; in addition, the magnetic field orientation follows the direction of the bendings. We interpret these features as possible indications of an interaction with the intracluster medium. This strengthens the hypothesis of positive AGN feedback, as inferred in previous studies of this object on the basis of X-ray/mm/radio analysis. In this scenario, the proto-BCG heats the surrounding medium and possibly enhances the SFR in nearby galaxies.

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arXiv2021

The AGN fuelling/feedback cycle in nearby radio galaxies -- IV. Molecular gas conditions and jet-ISM interaction in NGC3100

This is the fourth paper of a series investigating the AGN fuelling/feedback processes in a sample of eleven nearby low-excitation radio galaxies (LERGs). In this paper we present follow-up Atacama Large Millimeter/submillimeter Array (ALMA) observations of one source, NGC3100, targeting the $^{12}$CO(1-0), $^{12}$CO(3-2), HCO$^{+}$(4-3), SiO(3-2) and HNCO(6-5) molecular transitions. $^{12}$CO(1-0) and $^{12}$CO(3-2) lines are nicely detected and complement our previous $^{12}$CO(2-1) data. By comparing the relative strength of these three CO transitions, we find extreme gas excitation conditions (i.e. $T_{\rm ex}\gtrsim50$ K) in regions that are spatially correlated with the radio lobes, supporting the case for a jet-ISM interaction. An accurate study of the CO kinematics demonstrates that, although the bulk of the gas is regularly rotating, two distinct non-rotational kinematic components can be identified in the inner gas regions: one can be associated to inflow/outflow streaming motions induced by a two-armed spiral perturbation; the second one is consistent with a jet-induced outflow with $v_{\rm max}\approx 200$ km s$^{-1}$ and $\dot{M}\lesssim 0.12$ M$_{\odot}$ yr$^{-1}$. These values indicate that the jet-CO coupling ongoing in NGC3100 is only mildly affecting the gas kinematics, as opposed to what expected from existing simulations and other observational studies of (sub-)kpc scale jet-cold gas interactions. HCO$^{+}$(4-3) emission is tentatively detected in a small area adjacent to the base of the northern radio lobe, possibly tracing a region of jet-induced gas compression. The SiO(3-2) and HNCO(6-5) shock tracers are undetected: this - along with the tentative HCO$^{+}$(4-3) detection - may be consistent with a deficiency of very dense (i.e. $n_{\rm crit} > 10^{6}$ cm$^{-3}$) cold gas in the central regions of NGC3100.

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arXiv2021

The mm-to-cm SED of spiral galaxies. Synergies between NIKA2 and SRT instruments

The mm-to-cm range of the Spectral Energy Distribution of spiral galaxies remains largely unexplored. Its coverage is required to disentangle the contribution of dust emission, free-free and synchrotron radiation and can provide constraints on dust models, star-formation rates and ISM properties. We present the case for a synergy between NIKA2 observations of nearby spirals and those from planned and current instrumentation at the Sardinia Radio Telescope, and report on a pilot K-band program to search for Anomalous Microwave Emission, an elusive emission component which is presumably related to dust.

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arXiv2021

GASP XXXIV: Unfolding the thermal side of ram pressure stripping in the jellyfish galaxy JO201

X-ray studies of jellyfish galaxies play a crucial role in understanding the interactions between the interstellar medium (ISM) and the intracluster medium (ICM). In this paper, we focused on the jellyfish galaxy JO201. By combining archival Chandra observations, MUSE H$α$ cubes, and maps of the emission fraction of the diffuse ionised gas, we investigated both its high energy spectral properties and the spatial correlation between its X-ray and optical emissions. The X-ray emission of JO201 is provided by both the Compton thick AGN (L$_{\text{X}}^{0.5-10 \text{keV}}$=2.7$\cdot$10$^{41}$ erg s$^{-1}$, not corrected for intrinsic absorption) and an extended component (L$_{\text{X}}^{0.5-10 \, \text{keV}}\approx$1.9-4.5$\cdot$10$^{41}$ erg s$^{-1}$) produced by a warm plasma (kT$\approx$1 keV), whose luminosity is higher than expected from the observed star formation (L$_{\text{X}}\sim$3.8$\cdot10^{40}$ erg s$^{-1}$). The spectral analysis showed that the X-ray emission is consistent with the thermal cooling of hot plasma. These properties are similar to the ones found in other jellyfish galaxies showing extended X-ray emission. A point-to-point analysis revealed that this X-ray emission closely follows the ISM distribution, whereas CLOUDY simulations proved that the ionisation triggered by this warm plasma would be able to reproduce the [OI]/H$α$ excess observed in JO201. We conclude that the galactic X-ray emitting plasma is originated on the surface of the ISM as a result of the ICM-ISM interplay. This process would entail the cooling and accretion of the ICM onto the galaxy, which could additionally fuel the star formation, and the emergence of [OI]/H$α$ excess in the optical spectrum.

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arXiv2020

The LOFAR Two Metre Sky Survey: Deep Fields Data Release 1 -- III. Host-galaxy identifications and value added catalogues

We present the source associations, cross-identifications, and multi-wavelength properties of the faint radio source population detected in the deep tier of the LOFAR Two Metre Sky Survey (LoTSS): the LoTSS Deep Fields. The first LoTSS Deep Fields data release consists of deep radio imaging at 150~MHz of the ELAIS-N1, Lockman Hole, and Boötes fields, down to RMS sensitives of around 20, 22, and 32$~μ$Jy\,beam$^{-1}$, respectively. These fields are some of the best studied extra-galactic fields in the northern sky, with existing deep, wide-area panchromatic photometry from X-ray to infrared wavelengths, covering a total of $\approx$~26~\mbox{deg$^{2}$}. We first generated improved multi-wavelength catalogues in ELAIS-N1 and Lockman Hole; combined with the existing catalogue for Boötes, we present forced, matched aperture photometry for over 7.2 million sources across the three fields. We identified multi-wavelength counterparts to the radio detected sources, using a combination of the Likelihood Ratio method and visual classification, which greatly enhances the scientific potential of radio surveys and allows for the characterisation of the photometric redshifts and the physical properties of the host galaxies. The final radio-optical cross-matched catalogue consists of 81\,951 radio-detected sources, with counterparts identified and multi-wavelength properties presented for 79\,820 ($>$97\%) sources. We also examine the properties of the host galaxies, and through stacking analysis find that the radio population with no identified counterpart is likely dominated by AGN at $z\sim3-4$. This dataset contains one of the largest samples of radio-selected star-forming galaxies and active galactic nuclei (AGN) at these depths, making it ideal for studying the history of star-formation, and the evolution of galaxies and AGN across cosmic time.

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arXiv2020

Constraints on the [CII] luminosity of a proto-globular cluster at z~6 obtained with ALMA

We report on ALMA observations of D1, a system at z~6.15 with stellar mass M_* ~ 10^7 M_sun containing globular cluster (GC) precursors, strongly magnified by the galaxy cluster MACS J0416.1-2403. Since the discovery of GC progenitors at high redshift, ours is the first attempt to probe directly the physical properties of their neutral gas through infrared observations. A careful analysis of our dataset, performed with a suitable procedure designed to identify faint narrow lines and which can test various possible values for the unknown linewidth value, allowed us to identify a 4-sigma tentative detection of [CII] emission with intrinsic luminosity L_CII=(2.9 +/- 1.4) 10^6 L_sun, one of the lowest values ever detected at high redshift. This study offers a first insight on previously uncharted regions of the L_CII-SFR relation. Despite large uncertainties affecting our measure of the star formation rate, if taken at face value our estimate lies more than 1 dex below the values observed in local and high redshift systems. Our weak detection indicates a deficiency of [CII] emission, possibly ascribed to various explanations, such as a low-density gas and/or a strong radiation field caused by intense stellar feedback, and a low metal content. From the non-detection in the continuum we derive constraints on the dust mass, with 3-sigma upper limit values as low as a few 10^4 M_sun, consistent with the values measured in local metal-poor galaxies.

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arXiv2020

The AGN fuelling/feedback cycle in nearby radio galaxies III. 3D relative orientations of radio jets and CO discs and their interaction

This is the third paper of a series exploring the multi-frequency properties of a sample of eleven nearby low-excitation radio galaxies (LERGs) in the southern sky. We are conducting an extensive study of different galaxy components (stars, dust, warm and cold gas, radio jets) with the aim of better understanding the AGN fuelling/feedback cycle in LERGs. Here we present new, deep, sub-kpc resolution Karl G. Jansky Very Large Array (JVLA) data for five sample sources at 10 GHz. Coupling these data with previously-acquired Atacama Large Millimeter/submillimeter Array (ALMA) CO(2-1) observations and measurements of comparable quality from the literature, we carry out for the first time a full 3D analysis of the relative orientations of jet and disc rotation axes in six FR I LERGs. This analysis shows (albeit with significant uncertainties) that the relative orientation angles span a wide range ($\approx$30$^{\circ}-60^{\circ}$). There is no case where both axes are accurately aligned and there is a marginally significant tendency for jets to avoid the disc plane. Our study also provides further evidence for the presence of a jet-CO disc interaction (already inferred from other observational indicators) in at least one source, NGC 3100. In this case, the limited extent of the radio jets, along with distortions in both the molecular gas and the jet components, suggest that the jets are young, interacting with the surrounding matter and rapidly decelerating.

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arXiv2020

The high molecular gas content, and the efficient conversion of neutral into molecular gas, in jellyfish galaxies

In the disks of four jellyfish galaxies from the GASP sample at redshift $\sim 0.05$ we detect molecular gas masses systematically higher than in field galaxies. These galaxies are being stripped of their gas by ram pressure from the intra cluster medium and are, in general, forming stars at high rate with respect to non-stripped galaxies of similar stellar masses. We find that, unless giant molecular clouds in the disk are unbound by ram pressure leading to exceptionally high CO--to--$\rm H_2$ conversion factors, these galaxies have a molecular gas content 4-5 times higher than normal galaxies of similar masses, and molecular gas depletion times ranging from $\sim$1 to 9 Gyr, corresponding to generally very low star formation efficiencies. The molecular gas mass within the disk is a factor between 4 and $\sim$100 times higher than the neutral gas mass, as opposed to the disks of normal spirals that contain similar amounts of molecular and neutral gas. Intriguingly, the molecular plus neutral total amount of gas is similar to that in normal spiral galaxies of similar stellar mass. These results strongly suggest that ram pressure in disks of galaxies during the jellyfish phase leads to a very efficient conversion of HI into $\rm H_2$.

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arXiv2020

The Science Case for ALMA Band 2 and Band 2+3

We discuss the science drivers for ALMA Band 2 which spans the frequency range from 67 to 90 GHz. The key science in this frequency range are the study of the deuterated molecules in cold, dense, quiescent gas and the study of redshifted emission from galaxies in CO and other species. However, Band 2 has a range of other applications which are also presented. The science enabled by a single receiver system which would combine ALMA Bands 2 and 3 covering the frequency range 67 to 116 GHz, as well as the possible doubling of the IF bandwidth of ALMA to 16 GHz, are also considered.

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arXiv2019

GASP. XXII The molecular gas content of the JW100 jellyfish galaxy at z~0.05: does ram pressure promote molecular gas formation?

Within the GASP survey, aimed at studying the effect of the ram-pressure stripping on the star formation quenching in cluster galaxies, we analyze here ALMA observations of the jellyfish galaxy JW100. We find an unexpected large amount of molecular gas ($\sim 2.5 \times 10^{10} M_{\odot}$), 30\% of which is located in the stripped gas tail out to $\sim$35 kpc from the galaxy center. The overall kinematics of molecular gas is similar to the one shown by the ionized gas, but for clear signatures of double components along the stripping direction detected only out to 2 kpc from the disk. The line ratio $r_{21}$ has a clumpy distribution and in the tail can reach large values ($\geq 1$), while its average value is low (0.58 with a 0.15 dispersion). All these evidence strongly suggest that the molecular gas in the tail is newly born from stripped HI gas or newly condensed from stripped diffuse molecular gas. The analysis of interferometric data at different scales reveals that a significant fraction ($\sim 40\%$) of the molecular gas is extended over large scales ($\geq 8$ kpc) in the disk, and this fraction becomes predominant in the tail ($\sim 70\%$). By comparing the molecular gas surface density with the star formation rate surface density derived from the \Ha emission from MUSE data, we find that the depletion time on 1 kpc scale is particularly large ($5-10$ Gyr) both within the ram-pressure disturbed region in the stellar disk, and in the complexes along the tail.

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arXiv2019

GASP XVIII: Star formation quenching due to AGN feedback in the central region of a jellyfish galaxy

We report evidence for star formation quenching in the central 8.6 kpc region of the jellyfish galaxy JO201 which hosts an active galactic nucleus, while undergoing strong ram pressure stripping. The ultraviolet imaging data of the galaxy disk reveal a region with reduced flux around the center of the galaxy and a horse shoe shaped region with enhanced flux in the outer disk. The characterization of the ionization regions based on emission line diagnostic diagrams shows that the region of reduced flux seen in the ultraviolet is within the AGN-dominated area. The CO J$_{2-1}$ map of the galaxy disk reveals a cavity in the central region. The image of the galaxy disk at redder wavelengths (9050-9250 $\overset{\lower.5em\circ}{\mathrm{A}}$) reveals the presence of a stellar bar. The star formation rate map of the galaxy disk shows that the star formation suppression in the cavity occurred in the last few 10$^8$ yr. We present several lines of evidence supporting the scenario that suppression of star formation in the central region of the disk is most likely due to the feedback from the AGN. The observations reported here make JO201 a unique case of AGN feedback and environmental effects suppressing star formation in a spiral galaxy.

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arXiv2019

ALMA resolves the hourglass magnetic field in G31.41+0.31

Context. Submillimeter Array (SMA) 870 micron polarization observations of the hot molecular core G31.41+0.31 revealed one of the clearest examples up to date of an hourglass-shaped magnetic field morphology in a high-mass star-forming region. Aims. To better establish the role that the magnetic field plays in the collapse of G31.41+0.31, we carried out Atacama Large Millimeter/submillimeter Array (ALMA) observations of the polarized dust continuum emission at 1.3 mm with an angular resolution four times higher than that of the previous (sub)millimeter observations to achieve an unprecedented image of the magnetic field morphology. Methods. We used ALMA to perform full polarization observations at 233 GHz (Band 6). The resulting synthesized beam is 0.28"x0"20 which, at the distance of the source, corresponds to a spatial resolution of ~875 au. Results. The observations resolve the structure of the magnetic field in G31.41+0.31 and allow us to study the field in detail. The polarized emission in the Main core of G31.41+0.41is successfully fit with a semi-analytical magnetostatic model of a toroid supported by magnetic fields. The best fit model suggests that the magnetic field is well represented by a poloidal field with a possible contribution of a toroidal component of ~10% of the poloidal component, oriented southeast to northwest at ~ -44 deg and with an inclination of ~-45 degr. The magnetic field is oriented perpendicular to the northeast to southwest velocity gradient detected in this core on scales from 1E3-1E4 au. This supports the hypothesis that the velocity gradient is due to rotation and suggests that such a rotation has little effect on the magnetic field. The strength of the magnetic field estimated in the central region of the core with the Davis-Chandrasekhar-Fermi method is ~8-13 mG and implies that the mass-to-flux ratio in this region is slightly supercritical ...

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arXiv2019

Warped diffusive radio halo around the quiescent spiral edge-on galaxy NGC 4565

Cosmic rays play a pivotal role in launching galactic winds, particularly in quiescently star-forming galaxies where the hot gas alone is not sufficient to drive a wind. Except for the Milky Way, not much is known about the transport of cosmic rays in galaxies. In this Letter, we present low-frequency observations of the nearby edge-on spiral galaxy NGC 4565 using the LOw-Frequency ARray (LOFAR). With our deep 144-MHz observations, we obtain a clean estimate of the emission originating from old cosmic-ray electrons (CRe), which is almost free from contamination by thermal emission. We measured vertical profiles of the non-thermal radio continuum emission that we fitted with Gaussian and exponential functions. The different profile shapes correspond to 1D cosmic-ray transport models of pure diffusion and advection, respectively. We detect a warp in the radio continuum that is reminiscent of the previously known HI warp. Because the warp is not seen at GHz-frequencies in the radio continuum, its minimum age must be about 100 Myr. The warp also explains the slight flaring of the thick radio disc that can otherwise be well described by a Gaussian profile with an FWHM of 65 arcsec (3.7 kpc). The diffusive radio halo together with the extra-planar X-ray emission may be remnants of enhanced star-forming activity in the past where the galaxy had a galactic wind, as GHz-observations indicate only a weak outflow in the last 40 Myr. NGC 4565 could be in transition from an outflow- to an inflow-dominated phase.

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arXiv2019

A radio ridge connecting two galaxy clusters in a filament of the cosmic web

Galaxy clusters are the most massive gravitationally bound structures in the Universe. They grow by accreting smaller structures in a merging process that produces shocks and turbulence in the intra-cluster gas. We observed a ridge of radio emission connecting the merging galaxy clusters Abell 0399 and Abell 0401 with the Low Frequency Array (LOFAR) at 140 MHz. This emission requires a population of relativistic electrons and a magnetic field located in a filament between the two galaxy clusters. We performed simulations to show that a volume-filling distribution of weak shocks may re-accelerate a pre-existing population of relativistic particles, producing emission at radio wavelengths that illuminates the magnetic ridge.

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arXiv2019

Probing the cold magnetized Universe with SPICA-POL (B-BOP)

SPICA, the cryogenic infrared space telescope recently pre-selected for a `Phase A' concept study as one of the three remaining candidates for ESA's fifth medium class (M5) mission, is foreseen to include a far-infrared polarimetric imager (SPICA-POL, now called B-BOP), which would offer a unique opportunity to resolve major issues in our understanding of the nearby, cold magnetized Universe. This paper presents an overview of the main science drivers for B-BOP, including high dynamic range polarimetric imaging of the cold interstellar medium (ISM) in both our Milky Way and nearby galaxies. Thanks to a cooled telescope, B-BOP will deliver wide-field 100-350 micron images of linearly polarized dust emission in Stokes Q and U with a resolution, signal-to-noise ratio, and both intensity and spatial dynamic ranges comparable to those achieved by Herschel images of the cold ISM in total intensity (Stokes I). The B-BOP 200 micron images will also have a factor ~30 higher resolution than Planck polarization data. This will make B-BOP a unique tool for characterizing the statistical properties of the magnetized interstellar medium and probing the role of magnetic fields in the formation and evolution of the interstellar web of dusty molecular filaments giving birth to most stars in our Galaxy. B-BOP will also be a powerful instrument for studying the magnetism of nearby galaxies and testing galactic dynamo models, constraining the physics of dust grain alignment, informing the problem of the interaction of cosmic rays with molecular clouds, tracing magnetic fields in the inner layers of protoplanetary disks, and monitoring accretion bursts in embedded protostars.

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arXiv2018

ALMA polarimetric studies of rotating jet/disk systems

We have recently obtained polarimetric data at mm wavelengths with ALMA for the young systems DG Tau and CW Tau, for which the rotation properties of jet and disk have been investigated in previous high angular resolution studies. The motivation was to test the models of magneto-centrifugal launch of jets via the determination of the magnetic configuration at the disk surface. The analysis of these data, however, reveals that self-scattering of dust thermal radiation dominates the polarization pattern. It is shown that even if no information on the magnetic field can be derived in this case, the polarization data are a powerful tool for the diagnostics of the properties and the evolution of dust in protoplanetary disks.

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arXiv2018

Exploring the properties of low-frequency radio emission and magnetic fields in a sample of compact galaxy groups using the LOFAR Two-Metre Sky Survey (LoTSS)

We use the LOFAR Two-metre Sky Survey (LoTSS) Data Release I to identify the groups of galaxies (and individual galaxies) from the Hickson Compact Groups and Magnitude Limited Compact Groups samples that emit at the frequency of 150\,MHz, characterise their radio emission (extended or limited to the galaxies), and compare new results to earlier observations and theoretical predictions. The detection of 73 systems (and 7 more -- probably) out of 120, of which as many as 17 show the presence of extended radio structures, confirms the previous hypothesis of the common character of the magnetic field inside galaxy groups and its detectability. In order to investigate the future potential of low-frequency radio studies of galaxy groups, we also present a more detailed insight into four radio-emitting systems, for which the strength of the magnetic field inside their intergalactic medium (IGM) is calculated. The estimated values are comparable to that found inside star-forming galaxies, suggesting a dynamical and evolutionary importance of the magnetic field in galaxy groups.

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