arXiv subjects

Francesco Massaro

Publications and source records attributed to Francesco Massaro.

86 records · Page 5Linked to original sources

arXiv2021

The MURALES survey. IV. Searching for nuclear outflows in 3C radio galaxies at z < 0.3 with MUSE observations

We analyze VLT/MUSE observations of 37 radio galaxies from the Third Cambridge catalogue (3C) with redshift $<$0.3 searching for nuclear outflows of ionized gas. These observations are part of the MURALES project (a MUse RAdio Loud Emission line Snapshot survey), whose main goal is to explore the feedback process in the most powerful radio-loud AGN. We applied a nonparametric analysis to the [O~III] $λ$5007 emission line, whose asymmetries and high-velocity wings reveal signatures of outflows. We find evidence of nuclear outflows in 21 sources, with velocities between $\sim$400 - 1000 km s$^{-1}$, outflowing masses of $\sim 10^5-10^7$ M$_\odot$, and a kinetic energy in the range $\sim 10^{53} - 10^{56}$ erg. In addition, evidence for extended outflows is found in the 2D gas velocity maps of 13 sources of the subclasses of high-excitation (HEG) and broad-line (BLO) radio galaxies, with sizes between 0.4 and 20 kpc. We estimate a mass outflow rate in the range 0.4 - 30 M$_\odot$ yr$^{-1}$ and an energy deposition rate of ${\dot E}_{kin} \sim 10^{42}-10^{45} $ erg s$^{-1}$. Comparing the jet power, the nuclear luminosity of the active galactic nucleus, and the outflow kinetic energy rate, we find that outflows of HEGs and BLOs are likely radiatively powered, while jets likely only play a dominant role in galaxies with low excitation. The low loading factors we measured suggest that these outflows are driven by momentum and not by energy. Based on the gas masses, velocities, and energetics involved, we conclude that the observed ionized outflows have a limited effect on the gas content or the star formation in the host. In order to obtain a complete view of the feedback process, observations exploring the complex multiphase structure of outflows are required.

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arXiv2021

An optical overview of blazars with LAMOST I: Hunting changing-look blazars and new redshift estimates

The extragalactic $γ$-rays sky observed by Fermi-Large Area Telescope (LAT) is dominated by blazars. In the fourth release of the Fermi-LAT Point Source Catalog (4FGL), are sources showing a multifrequency behavior similar to that of blazars but lacking an optical spectroscopic confirmation of their nature known as Blazar Candidate of Uncertain type (BCUs). We aim at confirming the blazar nature of BCUs and test if new optical spectroscopic observations can reveal spectral features, allowing us to get a redshift estimate for known BL Lac objects. We also aim to search for and discover changing-look blazars (i.e., blazars that show a different classification at different epochs). We carried out an extensive search for optical spectra available in the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) Data Release 5 (DR5) archive. We selected sources out of the 4FGL catalog, the list of targets from our follow-up spectroscopic campaign of unidentified or unassociated $γ$-ray sources, and the multifrequency catalog of blazars: the Roma-BZCAT. We selected a total of 392 spectra. We also compare some of the LAMOST spectra with those available in the literature. We classified 20 BCUs confirming their blazar-like nature. Then we obtained 15 new redshift estimates for known blazars. We discovered 26 transitional (i.e., changing-look) blazars that changed their classification. Finally, we were able to confirm the blazar-like nature of six BL Lac candidates. All remaining sources analyzed agree with previous classifications. BL Lac objects are certainly the most elusive type of blazars in the $γ$-ray extragalactic sky.

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arXiv2020

Extended X-ray emission around FR II radio galaxies: hotspots, lobes and galaxy clusters

We present a systematic analysis of the extended X-ray emission discovered around 35 FR II radio galaxies from the revised Third Cambridge catalog (3CR) Chandra Snapshot Survey with redshifts between 0.05 to 0.9. We aimed to (i) test for the presence of extended X-ray emission around FR II radio galaxies, (ii) investigate if the extended emission origin is due to Inverse Compton scattering of seed photons arising from the Cosmic Microwave Background (IC/CMB) or to thermal emission from an intracluster medium (ICM) and (iii) test the impact of this extended emission on hotspot detection. We investigated the nature of the extended X-ray emission by studying its morphology and compared our results with low-frequency radio observations (i.e., $\sim$150 MHz), in the TGSS and LOFAR archives, as well as with optical images from Pan-STARRS. In addition, we optimized a search for X-ray counterparts of hotspots in 3CR FR II radio galaxies. We found statistically significant extended emission ($>$3$σ$ confidence level) along the radio axis for $\sim$90%, and in the perpendicular direction for $\sim$60% of our sample. We confirmed the detection of 7 hotspots in the 0.5 - 3 keV. In the cases where the emission in the direction perpendicular to the radio axis is comparable to that along the radio axis, we suggest that the underlying radiative process is thermal emission from ICM. Otherwise, the dominant radiative process is likely non-thermal IC/CMB emission from lobes. We found that non-thermal IC/CMB is the dominant process in $\sim$70% of the sources in our sample, while thermal emission from the ICM dominates in $\sim$15% of them.

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arXiv2020

The large-scale environment of FR 0 radio galaxies

We explore the properties of the large-scale environment of FR0 radio galaxies belonging to the FR0CAT sample which includes 104 compact radio sources associated with nearby (z<0.05) early-type galaxies. By using various estimators we find that FR0s live in regions of higher than the average galaxies density and a factor two lower density, on average, with respect to FRI radio galaxies. This latter difference is driven by the large fraction (63%) of FR0s located in groups formed by less than 15 galaxies, an environment which FRIs rarely (17%) inhabit. Beside the lack of substantial extended radio emission defining the FR0s class, this is the first significant difference between the properties of these two populations of low power radio galaxies. We interpret the differences in environment between FR0s and FRIs as the due to an evolutionary link between local galaxies density, BH spin, jet power, and extended radio emission.

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arXiv2020

On the physical association of Fermi-LAT blazars with their low-energy counterparts

Associating gamma-ray sources to their low-energy counterparts is one of the major challenges of modern gamma-ray astronomy. In the context of the Fourth Fermi Large Area Telescope Source Catalog (4FGL), the associations rely mainly on parameters as apparent magnitude, integrated flux, and angular separation between the gamma-ray source and its low-energy candidate counterpart. In this work we propose a new use of likelihood ratio and a complementary supervised learning technique to associate gamma-ray blazars in 4FGL, based only on spectral parameters as gamma-ray photon index, mid-infrared colors and radio-loudness. In the likelihood ratio approach, we crossmatch the WISE Blazar-Like Radio-Loud Sources catalog with 4FGL and compare the resulting candidate counterparts with the sources listed in the gamma-ray blazar locus to compute an association probability for 1138 counterparts. In the supervised learning approach, we train a random forest algorithm with 869 high confidence blazar associations and 711 fake associations, and then compute an association probability for 1311 candidate counterparts. A list with all 4FGL blazar candidates of uncertain type associated by our method is provided to guide future optical spectroscopic follow up observations.

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arXiv2020

Optical spectroscopic observations of gamma-ray blazar candidates. X. Results from the 2018--2019 SOAR and OAN-SPM observations of blazar candidates of uncertain type

The fourth Fermi Large Area Telescope Source Catalog (4FGL) lists over 5000 gamma-ray sources with statistical significance above 4$σ$. About 23% of the sources listed in this catalog are unidentified/unassociated gamma-ray sources while ~26% of the sources are classified as blazar candidates of uncertain type (BCUs), lacking optical spectroscopic information. To probe the blazar nature of candidate counterparts of UGSs and BCUs, we started our optical spectroscopic follow up campaign in 2012, which up to date account for more than 350 observed sources. In this paper, the tenth of our campaign, we report on the spectroscopic observations of 37 sources, mostly BCUs, whose observations were carried out predominantly at the Observatorio Astronómico Nacional San Pedro Mártir and the Southern Astrophysical Research Observatory between August 2018 and September 2019. We confirm the BL Lac nature of 27 sources and the flat spectrum radio quasar nature of three sources. The remaining ones are classified as six BL Lacs galaxy-dominated and one normal galaxy. We were also able to measure the redshifts for 20 sources, including 10 BL Lacs. As in previous analyses, the largest fraction of BCUs revealed to be BL Lac objects.

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arXiv2019

Optical characterization of WISE selected blazar candidates

Over the last decade more than five thousand gamma-ray sources were detected by the Large Area Telescope (LAT) on board Fermi Gamma-ray Space Telescope. Given the positional uncertainty of the telescope, nearly 30% of these sources remain without an obvious counterpart in lower energies. This motivated the release of new catalogs of gamma-ray counterpart candidates and several follow up campaigns in the last decade. Recently, two new catalogs of blazar candidates were released, they are the improved and expanded version of the WISE Blazar-Like Radio-Loud Sources (WIBRaLS2) catalog and the Kernel Density Estimation selected candidate BL Lacs (KDEBLLACS) catalog, both selecting blazar-like sources based on their infrared colors from the Wide-field Infrared Survey Explorer (WISE). In this work we characterized these two catalogs, clarifying the true nature of their sources based on their optical spectra from SDSS data release 15, thus testing how efficient they are in selecting true blazars. We first selected all WIBRaLS2 and KDEBLLACS sources with available optical spectra in the footprint of Sloan Digital Sky Survey data release 15. Then we analyzed these spectra to verify the nature of each selected candidate and see which fraction of the catalogs is composed by spectroscopically confirmed blazars. Finally, we evaluated the impact of selection effects, specially those related to optical colors of WIBRaLS2/KDEBLLACS sources and their optical magnitude distributions. We found that at least ~ 30% of each catalog is composed by confirmed blazars, with quasars being the major contaminants in the case of WIBRaLS2 (~ 58%) and normal galaxies in the case of KDEBLLACS (~ 38.2%). The spectral analysis also allowed us to identify the nature of 11 blazar candidates of uncertain type (BCUs) from the Fermi-LAT 4th Point Source Catalog (4FGL) and to find 25 new BL Lac objects.

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arXiv2019

COMP2CAT: hunting compact double radio sources in the local Universe

We present a catalog of compact double radio galaxies (hereafter COMP2$CAT$) listing 43 edge-brightened radio sources whose projected linear size does not exceed 60 kpc, the typical size of their host galaxies. This is the fifth in a series of radio source catalogs recently created, namely: FRI$CAT$, FRII$CAT$, FR0$CAT$ and WAT$CAT$, each focused on a different class of radio galaxies. The main aim of our analysis is to attain a better understanding of sources with intermediate morphologies between FR\,IIs and FR\,0s. COMP2$CAT$ sources were selected from an existing catalog of radio sources based on NVSS, FIRST and SDSS observations for having, mainly, i) edge-brightened morphologies, typical of FR\,IIs, ii) redshifts $z < 0.15$ and iii) projected linear sizes smaller than 60 kpc. With radio luminosities at 1.4 GHz $10^{38} \lesssim L_{1.4} \lesssim 10^{41}$ erg s$^{-1}$, COMP2$CAT$ sources appear as the low radio luminosity tail of FR\,IIs. However, their host galaxies are indistinguishable from those of large-scale radio sources: they are luminous ($-21 \gtrsim M_{r} \gtrsim -24$), red, early-type galaxies with black hole masses in the range of $10^{7.5} \lesssim M_{\rm BH} \lesssim 10^{9.5}\, \rm{M}_\odot$. Moreover, all but one of the COMP2$CAT$ sources are optically classifiable as low excitation radio galaxies, in agreement with being the low radio-power tail of FR\,Is and FR\,IIs. This catalog of compact double sources, which is $\sim 47 \%$ complete at $z<0.15$, can potentially be used to clarify the role of compact double sources in the general evolutionary scheme of radio galaxies.

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arXiv2019

Two new catalogs of blazar candidates in the WISE infrared sky

We present two catalogs of radio-loud candidate blazars whose WISE mid-infrared colors are selected to be consistent with the colors of confirmed gamma-ray emitting blazars. The first catalog is the improved and expanded release of the WIBRaLS catalog presented by D'Abrusco et al. (2014): it includes sources detected in all four WISE filters, spatially cross-matched with radio source in one of three radio surveys and radio-loud based on their q22 spectral parameter. WIBRaLS2 includes 9541 sources classified as BL Lacs, FSRQs or mixed candidates based on their WISE colors. The second catalog, called KDEBLLACS, based on a new selection technique, contains 5579 candidate BL Lacs extracted from the population of WISE sources detected in the first three WISE passbands ([3.4], [4.6] and [12]) only, whose mid-infrared colors are similar to those of confirmed, gamma-ray BL Lacs. KDBLLACS members area also required to have a radio counterpart and be radio-loud based on the parameter q12, defined similarly to q22 used for the WIBRaLS2. We describe the properties of these catalogs and compare them with the largest samples of confirmed and candidate blazars in the literature. We crossmatch the two new catalogs with the most recent catalogs of gamma-ray sources detected by Fermi LAT instrument. Since spectroscopic observations of candidate blazars from the first WIBRaLS catalog within the uncertainty regions of gamma-ray unassociated sources confirmed that ~90% of these candidates are blazars, we anticipate that these new catalogs will play again an important role in the identification of the gamma-ray sky.

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arXiv2018

3C 17: The BCG of a galaxy cluster at z=0.22

Gemini Multi Object Spectrograph medium-resolution spectra and photometric data of 39 objects in the field of the radio galaxy 3C 17 are presented. Based on the new data, a previously uncataloged cluster of galaxies is identified at a mean redshift of z=0.220 +/-0.003, a projected virial radius of 0.37 Mpc, and a velocity dispersion of sigma_v = 821 +/-171 km/s. The brightest member of this cluster is 3C 17 with M_r = -22.45 mag. The surface brightness profile of 3C 17 is best fit with two components (Exponential + Sersic) characteristic of brightest cluster galaxies. The spectrum of 3C 17 is dominated by broad emission lines Halpha + N[II] and Hbeta + [OIII]. Analysis of Chandra data shows extended emission around the cluster core that supports the existence of hot gas cospatial with 3C 17. The discovery of a cluster of galaxies around 3C 17 better explains the sharply bent morphology of the radio jet given that it propagates through a dense intracluster medium.

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arXiv2017

A Multi-band Study of the remarkable Jet in Quasar 4C+19.44

We present arc-second-resolution data in the radio, IR, optical and X-ray for 4C+19.44 (=PKS 1354+195), the longest and straightest quasar jet with deep X-ray observations. We report results from radio images with half to one arc-second angular resolution at three frequencies, plus HST and Spitzer data. The Chandra data allow us to measure the X-ray spectral index in 10 distinct regions along the 18 arcsec jet and compare with the radio index. The radio and X-ray spectral indices of the jet regions are consistent with a value of $α=0.80$ throughout the jet, to within 2 sigma uncertainties. The X-ray jet structure to the south extends beyond the prominent radio jet and connects to the southern radio lobe, and there is extended X-ray emission in the direction of the unseen counter jet and coincident with the northern radio lobe. This jet is remarkable since its straight appearance over a large distance allows the geometry factors to be taken as fixed along the jet. Using the model of inverse Compton scattering of the cosmic microwave background (iC/CMB) by relativistic electrons, we find that the magnetic field strengths and Doppler factors are relatively constant along the jet. If instead the X-rays are synchrotron emission, they must arise from a population of electrons distinct from the particles producing the radio synchrotron spectrum.

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arXiv2016

A Comprehensive Statistical Description of Radio-Through-$γ$-Ray Spectral Energy Distributions of All Known Blazars

We combined multi-wavelength data for blazars from the Roma-BZCAT catalog and analyzed hundreds of X-ray spectra. We present the fluxes and Spectral Energy Distributions (SEDs), in 12 frequency bands from radio to $γ$-rays, for a final sample of 2214 blazars. Using a model-independent statistical approach, we looked for systematic trends in the SEDs; the most significant trends involved the radio luminosities and X-ray spectral indices of the blazars. We used a Principal Component Analysis (PCA), to determine the basis vectors of the blazar SEDs and, in order to maximize the size of the sample, imputed missing fluxes using the K-nearest neighbors method. Using more than an order of magnitude more data than was available when Fossati et al. (1997, 1998) first reported trends of SED shape with blazar luminosity, we confirmed the anti-correlation between radio luminosity and synchrotron peak frequency, although with greater scatter than was seen in the smaller sample. The same trend can be seen between bolometric luminosity and synchrotron peak frequency. Finally, we used all available blazar data to determine an empirical SED description that depends only on the radio luminosity at 1.4~GHz and the redshift. We verified that this statistically significant relation was not a result of the luminosity-luminosity correlations that are natural in flux-limited samples (i.e., where the correlation is actually caused by the redshift rather than the luminosity).

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arXiv2016

Shocking Features in the Merging Galaxy Cluster RXJ0334.2-0111

We present a 66 ksec $\textit{Chandra}$ X-ray observation of the galaxy cluster RXJ0334.2-0111. This deep observation revealed a unique bow shock system associated with a wide angle tail (WAT) radio galaxy and several intriguing substructures. The temperature across the bow shock jumps by a factor of $\sim$ 1.5 (from 4.1 keV to 6.2 keV), and is consistent with the Mach number $M = 1.6_{-0.3}^{+0.5}$. A second inner surface brightness edge is a cold front that marks the border between infalling subcluster cool core and the ICM of the main cluster. The temperature across the cold front increases from $1.3_{-0.8}^{+0.3}$ keV to $6.2_{-0.6}^{+0.6}$ keV. We find an overpressurized region $\sim$ 250 kpc east of the cold front that is named "the eastern extension (EE)". The EE may be a part of the third subcluster in the ongoing merger. We also find a tail shaped feature that originates near the bow shock and may extend up to a distance of $\sim$ 1 Mpc. This feature is also likely overpressurized. The luminous FR-I radio galaxy, 3C89, appears to be the cD galaxy of the infalling subcluster. We estimated 3C89's jet power from jet bending and the possible interaction between the X-ray gas and the radio lobes. A comparison between the shock stand-off distance and the Mach number for all known shock front/cold front combinations suggests that the core is continuously shrinking in size by stripping.

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arXiv2013

Discovery of GeV Emission from the Circinus galaxy with the Fermi-LAT

We report the discovery of gamma-ray emission from the Circinus galaxy using the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope. Circinus is a nearby (~4 Mpc) starburst with a heavily obscured Seyfert-type active nucleus, bipolar radio lobes perpendicular to the spiral disk, and kpc-scale jet-like structures. Our analysis of 0.1-100 GeV events collected during 4 years of LAT observations reveals a significant (~ 7.3 sigma) excess above the background. We find no indications of variability or spatial extension beyond the LAT point-spread function. A power-law model used to describe the 0.1-100 GeV gamma-ray spectrum yields a flux of (18.8+/-5.8)x10^{-9} ph cm^{-2} s^{-1} and photon index 2.19+/-0.12, corresponding to an isotropic gamma-ray luminosity of 3 x 10^{40} erg s^{-1}. This observed gamma-ray luminosity exceeds the luminosity expected from cosmic-ray interactions in the interstellar medium and inverse Compton radiation from the radio lobes. Thus the origin of the GeV excess requires further investigation.

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