Publication Search Results

ID: 159641
Type: article
Authors: Jimenez-Gallardo, A.; Massaro, F.; Paggi, A.; D'Abrusco, Raffaele; Prieto, M. A.; Peña-Herazo, H. A.; Berta, V.; Ricci, F.; Stuardi, C.; Wilkes, Belinda J.; O'Dea, C. P.; Baum, S. A.; Kraft, Ralph P.; Forman, William R.; Jones-Forman, Christine; Mingo, B.; Liuzzo, E.; Balmaverde, B.; Capetti, A.; Missaglia, V.; Hardcastle, M. J.; Baldi, R. D.; Morabito, L. K.
Abstract: 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 and 0.9. We aimed to (i) test for the presence of extended X-ray emission around FR II radio galaxies, (ii) investigate whether the extended emission origin is due to inverse Compton (IC) scattering of seed photons arising from the cosmic microwave background (CMB) or thermal emission from an intracluster medium (ICM), and (iii) test the impact of this extended emission on hot-spot 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., ∼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 hot spots in 3CR FR II radio galaxies. We found statistically significant extended emission (>3σ confidence level) along the radio axis of ∼90% and in the perpendicular direction of ∼60% of the galaxies in our sample. We confirmed the detection of seven hot spots in the 0.5-3 keV energy range. 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 the ICM. Otherwise, the dominant radiative process is likely nonthermal IC/CMB emission from lobes. We found that nonthermal IC/CMB is the dominant process in ∼70% of the sources in our sample, while thermal emission from the ICM dominates in ∼15% of them.

ID: 157800
Type: article
Authors: Cantiello, Michele; Venhola, Aku; Grado, Aniello; Paolillo, Maurizio; D'Abrusco, Raffaele; Raimondo, Gabriella; Quintini, Massimo; Hilker, Michael; Mieske, Steffen; Tortora, Crescenzo; Spavone, Marilena; Capaccioli, Massimo; Iodice, Enrica; Peletier, Reynier; Barroso, Jesús Falcón; Limatola, Luca; Napolitano, Nicola; Schipani, Pietro; van de Ven, Glenn; Gentile, Fabrizio; Covone, Giovanni
Abstract: Context. A possible pathway for understanding the events and the mechanisms involved in galaxy formation and evolution is an in-depth investigation of the galactic and inter-galactic fossil sub-structures with long dynamical timescales: stars in the field and in stellar clusters.
Aims: This paper continues the Fornax Deep Survey (FDS) series. Following previous studies dedicated to extended Fornax cluster members, we present the catalogs of compact stellar systems in the Fornax cluster, as well as extended background sources and point-like sources.
Methods: We derived ugri photometry of ∼1.7 million sources over the ∼21 square degree area of FDS centered on the bright central galaxy NGC 1399. For a wider area, of ∼27 square degrees extending in the direction of NGC 1316, we provided gri photometry for ∼3.1 million sources. To improve the morphological characterization of sources, we generated multi-band image stacks by coadding the best-seeing gri-band single exposures with a cut at full width at half maximum (FWHM) ≤ 0.″9. We used the multi-band stacks as master detection frames, with a FWHM improved by ∼15% and a FWHM variability from field to field reduced by a factor of ∼2.5 compared to the pass-band with the best FWHM, namely the r-band. The identification of compact sources, in particular, globular clusters (GC), was obtained from a combination of photometric (e.g., colors, magnitudes) and morphometric (e.g., concentration index, elongation, effective radius) selection criteria, also taking as reference the properties of sources with well-defined classifications from spectroscopic or high-resolution imaging data.
Results: Using the FDS catalogs, we present a preliminary analysis of GC distributions in the Fornax area. The study confirms and extends further previous results that were limited to a smaller survey area. We observed the inter-galactic population of GCs, a population of mainly blue GCs centered on NGC 1399, extending over ∼0.9 Mpc, with an ellipticity ∊ ∼ 0.65 and a small tilt in the direction of NGC 1336. Several sub-structures extend over ∼0.5 Mpc along various directions. Two of these structures do not cross any bright galaxy; one of them appears to be connected to NGC 1404, a bright galaxy close to the cluster core and particularly poor in GCs. Using the gri catalogs, we analyze the GC distribution over the extended FDS area and do not find any obvious GC sub-structure bridging the two brightest cluster galaxies, namely, NGC 1316 and NGC 1399. Although NGC 1316 is more than twice as bright of NGC 1399 in optical bands, using gri data, we estimate a GC population that is richer by a factor of ∼3-4 around NGC 1399, as compared to NGC 1316, out to galactocentric distances of ∼40' or ∼230 kpc.
Full Tables 3-6 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/639/A136

ID: 156234
Type: article
Authors: de Menezes, R.; Amaya-Almazán, R. A.; Marchesini, E. J.; Peña-Herazo, H. A.; Massaro, F.; Chavushyan, V.; Paggi, A.; Landoni, M.; Masetti, N.; Ricci, F.; D'Abrusco, Raffaele; La Franca, F.; Smith, Howard A.; Milisavljevic, D.; Tosti, G.; Jiménez-Bailón, E.; Cheung, C. C.
Abstract: The fourth Fermi Large Area Telescope Source Catalog (4FGL) lists over 5000 γ -ray sources with statistical significance above 4 σ . About 23% of the sources listed in this catalog are unidentified/unassociated γ -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.

ID: 157801
Type: article
Authors: de Menezes, Raniere; D'Abrusco, Raffaele; Massaro, Francesco; Gasparrini, Dario; Nemmen, Rodrigo
Abstract: Associating γ-ray sources to their low-energy counterparts is one of the major challenges of modern γ-ray astronomy. In the context of the Fourth Fermi Large Area Telescope Source Catalog (4FGL), the associations rely mainly on parameters such as apparent magnitude, integrated flux, and angular separation between the γ-ray source and its low-energy candidate counterpart. In this work, we propose a new use of the likelihood ratio (LR) and a complementary supervised learning technique to associate γ-ray blazars in 4FGL, based only on spectral parameters such as the γ-ray photon index, mid-infrared colors, and radio-loudness. In the LR approach, we crossmatch the Wide-field Infrared Survey Explorer Blazar-Like Radio-Loud Sources catalog with 4FGL and compare the resulting candidate counterparts with the sources listed in the γ-ray blazar locus to compute an association probability (AP) 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 AP 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.

ID: 155834
Type: article
Authors: Kim, Dong-Woo; Traynor, Liam; Paggi, Alessandro; O'Sullivan, Ewan; Anderson, Craig; Burke, Douglas; D'Abrusco, Raffaele; Fabbiano, Giuseppina; Fruscione, Antonella; Lauer, Jennifer; McCollough, Michael; Morgan, Douglas; Mossman, Amy; Vrtilek, Saeqa; Trinchieri, Ginevra
Abstract: Using the data products of the Chandra Galaxy Atlas (Kim et al.), we have investigated the radial profiles of the hot gas temperature in 60 early-type galaxies (ETGs). Considering the characteristic temperature and radius of the peak, dip, and break (when scaled by the gas temperature and virial radius of each galaxy), we propose a universal temperature profile of the hot halo in ETGs. In this scheme, the hot gas temperature peaks at R_MAX = 35 ± 25 kpc (or ∼0.04 R_VIR) and declines both inward and outward. The temperature dips (or breaks) at R_MIN (or R_BREAK) = 3-5 kpc (or ∼0.006 R_VIR). The mean slope between R_MIN (R_BREAK) and R_MAX is 0.3 ± 0.1. Allowing for selection effects and observational limits, we find that the universal temperature profile can describe the temperature profiles of 72 per cent (possibly up to 82 per cent) of our ETG sample. The remaining ETGs (18 per cent) with irregular or monotonically declining profiles do not fit the universal profile and require another explanation. The temperature gradient inside R_MIN (R_BREAK) varies widely, indicating different degrees of additional heating at small radii. Investigating the nature of the hot core (HC with a negative gradient inside R_MIN), we find that HC is most clearly visible in small galaxies. Searching for potential clues associated with stellar, active galactic nucleus (AGN) feedback, and gravitational heating, we find that HC may be related to recent star formation. But we see no clear evidence that AGN feedback and gravitational heating play any significant role for HC.

ID: 158785
Type: article
Authors: Peña-Herazo, H. A.; Amaya-Almazán, R. A.; Massaro, F.; de Menezes, R.; Marchesini, E. J.; Chavushyan, V.; Paggi, A.; Landoni, M.; Masetti, N.; Ricci, F.; D'Abrusco, Raffaele; Cheung, C. C.; La Franca, F.; Smith, H. A.; Milisavljevic, D.; Jiménez-Bailón, E.; Patiño-Álvarez, V. M.; Tosti, G.
Abstract: Context. A significant fraction of all ?-ray sources detected by the Large Area Telescope aboard the Fermi satellite is still lacking a low-energy counterpart. In addition, there is still a large population of ?-ray sources with associated low-energy counterparts that lack firm classifications. In the last 10 years we have undertaken an optical spectroscopic campaign to address the problem of unassociated or unidentified ?-ray sources (UGSs), mainly devoted to observing blazars and blazar candidates because they are the largest population of ?-ray sources associated to date.
Aims: Here we describe the overall impact of our optical spectroscopic campaign on sources associated in Fermi-LAT catalogs, coupled with objects found in the literature. In the literature search we kept track of efforts by different teams that presented optical spectra of counterparts or potential counterparts of Fermi-LAT catalog sources. Our summary includes an analysis of additional 30 newly collected optical spectra of counterparts or potential counterparts of Fermi-LAT sources of a previously unknown nature.
Methods: New spectra were acquired at the Blanco 4 m and OAN-SPM 2.1 m telescopes, and those available in the Sloan Digital Sky Survey (data release 15) archive.
Results: All new sources with optical spectra analyzed here are classified as blazars. Thanks to our campaign, altogether we discovered and classified 394 targets with an additional 123 objects collected from a literature search. We began our optical spectroscopic campaign between the release of the second and third Fermi-LAT source catalogs (2FGL and 3FGL, respectively), classified about 25% of the sources that had uncertain nature and discovered a blazar-like potential counterpart for ˜10% of UGSs listed therein. In the 4FGL catalog, about 350 Fermi-LAT sources have been classified to date thanks to our campaign.
Conclusions: The most elusive class of blazars are found to be BL Lacs since the largest fraction of Fermi-LAT sources targeted in our observations showed a featureless optical spectrum. The same conclusion applied to the literature spectra. Finally, we confirm the high reliability of mid-IR color-based methods to select blazar-like candidate counterparts of unassociated or unidentified ?-ray sources.
Full Tables B.1 and B.2 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/643/A103

ID: 157799
Type: article
Authors: Venhola, Aku; Peletier, Reynier; Laurikainen, Eija; Salo, Heikki; Iodice, Enrichetta; Mieske, Steffen; Hilker, Michael; Wittmann, Carolin; Lisker, Thorsten; Paolillo, Maurizio; Cantiello, Michele; Janz, Joachim; Spavone, Marilena; D'Abrusco, Raffaele; Ven, Glennvande; Napolitano, Nicola; Kleijn, Gijs Verdoes; Maddox, Natasha; Capaccioli, Massimo; Grado, Aniello; Valentijn, Edwin; Falcón-Barroso, Jesús; Limatola, Luca
Abstract: This article is an erratum for:[https://doi.org/10.1051/0004-6361/201833933]

ID: 155678
Type: article
Authors: Venhola, Aku; Peletier, Reynier; Laurikainen, Eija; Salo, Heikki; Iodice, Enrichetta; Mieske, Steffen; Hilker, Michael; Wittmann, Carolin; Paolillo, Maurizio; Cantiello, Michele; Janz, Joachim; Spavone, Marilena; D'Abrusco, Raffaele; van de Ven, Glenn; Napolitano, Nicola; Verdoes Kleijn, Gijs; Capaccioli, Massimo; Grado, Aniello; Valentijn, Edwin; Falcón-Barroso, Jesús; Limatola, Luca

ID: 154556
Type: article
Authors: Angora, G.; Brescia, M.; Cavuoti, S.; Paolillo, M.; Longo, G.; Cantiello, M.; Capaccioli, M.; D'Abrusco, Raffaele; D'Ago, G.; Hilker, M.; Iodice, E.; Mieske, S.; Napolitano, N.; Peletier, R.; Pota, V.; Puzia, T.; Riccio, G.; Spavone, M.
Abstract: In the last years, Astroinformatics has become a well-defined paradigm for many fields of Astronomy. In this work, we demonstrate the potential of a multidisciplinary approach to identify globular clusters (GCs) in the Fornax cluster of galaxies taking advantage of multiband photometry produced by the VLT Survey Telescope using automatic self-adaptive methodologies. The data analysed in this work consist of deep, multiband, partially overlapping images centred on the core of the Fornax cluster. In this work, we use a Neural Gas model, a pure clustering machine learning methodology, to approach the GC detection, while a novel feature selection method (ΦLAB) is exploited to perform the parameter space analysis and optimization. We demonstrate that the use of an Astroinformatics-based methodology is able to provide GC samples that are comparable, in terms of purity and completeness with those obtained using single-band HST data and two approaches based, respectively, on a morpho-photometric and a Principal Component Analysis using the same data discussed in this work.

ID: 151855
Type: article
Authors: D'Abrusco, Raffaele; Álvarez Crespo, Nuria; Massaro, Francesco; Campana, Riccardo; Chavushyan, Vahram; Landoni, Marco; La Franca, Fabio; Masetti, Nicola; Milisavljevic, Dan; Paggi, Alessandro; Ricci, Federica; Smith, Howard A.
Abstract: We present two catalogs of radio-loud candidate blazars whose Wide-Field Infrared Survey Explorer (WISE) mid-infrared colors are selected to be consistent with the colors of confirmed γ-ray-emitting blazars. The first catalog is the improved and expanded release of the WISE Blazar-like Radio-Loud Sources (WIBRaLS) catalog presented by D'Abrusco et al. It includes sources detected in all four WISE filters, spatially cross-matched with radio sources in one of three radio surveys and radio-loud based on their q ₂₂ spectral parameter. WIBRaLS2 includes 9541 sources classified as BL Lacs, flat-spectrum radio quasars, 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, γ-ray BL Lacs. Members of KDBLLACS are also required to have a radio counterpart and be radio-loud based on the parameter q ₁₂, defined similarly to the q ₂₂ 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 cross-match the two new catalogs with the most recent catalogs of γ-ray sources detected by the Fermi Large Area Telescope. Since spectroscopic observations of candidate blazars from the first WIBRaLS catalog within the uncertainty regions of γ-ray unassociated sources confirmed that ∼90% of these candidates are blazars, we anticipate that these new catalogs will again play an important role in the identification of the γ-ray sky.

ID: 154630
Type: article
Authors: de Menezes, Raniere; Peña-Herazo, Harold A.; Marchesini, Ezequiel J.; D'Abrusco, Raffaele; Masetti, Nicola; Nemmen, Rodrigo; Massaro, Francesco; Ricci, Federica; Landoni, Marco; Paggi, Alessandro; Smith, Howard A.
Abstract: Context. Over the last decade more than five thousand γ-ray sources have been detected by the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope. Given the positional uncertainty of the telescope, nearly 30% of these sources remain without an obvious counterpart at lower energies. This has motivated the release of new catalogs of γ-ray counterpart candidates and several follow up campaigns in the last decade.
Aims: Recently, two new catalogs of blazar candidates were released. These 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 characterize these two catalogs, clarifying the true nature of their sources based on their optical spectra from SDSS data release 15, thus testing their efficiency in selecting true blazars.
Methods: We first selected all WIBRaLS2 and KDEBLLACS sources with available optical spectra in the footprint of Sloan Digital Sky Survey data release 15. We then analyzed these spectra to verify the nature of each selected candidate and to measure the fraction of the catalogs composed by spectroscopically confirmed blazars. Finally, we evaluated the impact of selection effects, especially those related to optical colors of WIBRaLS2/KDEBLLACS sources and their optical magnitude distributions.
Results: We found that at least ̃30% of each catalog is made up of 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 fourth Point Source Catalog (4FGL) and to find 25 new BL Lac objects.

ID: 150910
Type: article
Authors: Iodice, E.; Spavone, M.; Capaccioli, M.; Peletier, R. F.; van de Ven, G.; Napolitano, N. R.; Hilker, M.; Mieske, S.; Smith, R.; Pasquali, A.; Limatola, L.; Grado, A.; Venhola, A.; Cantiello, M.; Paolillo, M.; Falcon-Barroso, J.; D'Abrusco, Raffaele; Schipani, P.
Abstract: Context. This paper is based on the multi-band (ugri) Fornax Deep Survey (FDS) with the VLT Survey Telescope (VST). We study bright early-type galaxies (m_B ≤ 15 mag) in the 9 square degrees around the core of the Fornax cluster, which covers the virial radius (R_vir ˜ 0.7 Mpc).
Aims: The main goal of the present work is to provide an analysis of the light distribution for all galaxies out to unprecedented limits (in radius and surface brightness) and to release the main products resulting from this analysis in all FDS bands. We give an initial comprehensive view of the galaxy structure and evolution as a function of the cluster environment.
Methods: From the isophote fit, we derived the azimuthally averaged surface brightness profiles, the position angle, and ellipticity profiles as a function of the semi-major axis. In each band, we derived the total magnitudes, effective radii, integrated colours, and stellar mass-to-light ratios.
Results: The long integration times, the arcsec-level angular resolution of OmegaCam at VST, and the large covered area of FDS allow us to map the light and colour distributions out to large galactocentric distances (up to about 10-15 R_e) and surface brightness levels beyond μ_r = 27 mag arcsec^-2 (μ_B ≥ 28 mag arcsec^-2). Therefore, the new FDS data allow us to explore in great detail the morphology and structure of cluster galaxies out to the region of the stellar halo. The analysis presented in this paper allows us to study how the structure of galaxies and the stellar population content vary with the distance from the cluster centre. In addition to the intra-cluster features detected in previous FDS works, we found a new faint filament between FCC 143 and FCC 147, suggesting an ongoing interaction.
Conclusions: The observations suggest that the Fornax cluster is not completely relaxed inside the virial radius. The bulk of the gravitational interactions between galaxies happens in the W-NW core region of the cluster, where most of the bright early-type galaxies are located and where the intra-cluster baryons (diffuse light and globular clusters) are found. We suggest that the W-NW sub-clump of galaxies results from an infalling group onto the cluster, which has modified the structure of the galaxy outskirts (making asymmetric stellar halos) and has produced the intra-cluster baryons (ICL and GCs), concentrated in this region of the cluster. The tables and profiles resulting from the isophote fit are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/623/A1

ID: 155313
Type: article
Authors: Kim, Dong-Woo; Anderson, Craig S.; Burke, Douglas J.; D'Abrusco, Raffaele; Fabbiano, Giuseppina; Fruscione, Antonella; Lauer, Jennifer; McCollough, Michael; Morgan, Douglas; Mossman, Amy; O'Sullivan, Ewan; Paggi, Alessandro; Vrtilek, Saeqa; Trinchieri, Ginevra
Abstract: The hot interstellar medium (ISM) in early-type galaxies (ETGs) plays a crucial role in understanding their formation and evolution. The structural features of the hot gas identified by Chandra observations point to key evolutionary mechanisms, (e.g., active galactic nuclei, AGN, and stellar feedback, merging history). In our Chandra Galaxy Atlas (CGA) project, taking full advantage of the Chandra capabilities, we systematically analyzed the archival Chandra data of 70 ETGs and produced uniform data products for the hot gas properties. The primary data products are spatially resolved 2D spectral maps of the hot gas from individual galaxies. We emphasize that new features can be identified in the spectral maps that are not readily visible in the surface brightness maps. The high-level images can be viewed at the dedicated CGA website, and the CGA data products can be downloaded to compare with data at other wavelengths and to perform further analyses. Using our data products, we address a few focused science topics.

ID: 154594
Type: article
Authors: Marchesini, E. J.; Paggi, A.; Massaro, F.; Masetti, N.; D'Abrusco, Raffaele; Andruchow, I.; de Menezes, R.
Abstract: Context. BL Lac objects are an extreme type of active galactic nuclei (AGNs) that belong to the largest population of γ-ray sources: blazars. This class of AGNs shows a double-bumped spectral energy distribution that is commonly described in terms of a synchrotron self-Compton (SSC) emission process, whereas the low-energy component that dominates their emission between the infrared and the X-ray band is tightly connected to the high-energy component that peaks in the γ-rays. Two strong connections that link radio and mid-infrared emission of blazars to the emission in the γ-ray band are well established. They constitute the basis for associating γ-ray sources with their low-energy counterparts. Aims: We searched for a possible link between X-ray and γ-ray emissions for the subclass of BL Lacs using all archival Swift/XRT observations combined with Fermi data for a selected sample of 351 sources. Methods: Analyzing ̃2400 ks of Swift/XRT observations that were carried out until December 2018, we discovered that above the γ-ray flux threshold F_γ ≈ 3 × 10^-12 erg cm^-2 s^-1, 96% of all Fermi BL Lacs have an X-ray counterpart that is detected with signal-to-noise ratio > 3. Results: We did not find any correlation or clear trend between X-ray and γ-ray fluxes and/or spectral shapes, but we discovered a correlation between the X-ray flux and the mid-infrared color. Finally, we discuss on a possible interpretation of our results in the SSC framework. Full Table 1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz- bin/cat/J/A+A/631/A150

ID: 150415
Type: article
Authors: Marchesini, E. J.; Peña-Herazo, H. A.; Álvarez Crespo, N.; Ricci, Federica; Negro, M.; Milisavljevic, D.; Massaro, F.; Masetti, N.; Landoni, M.; Chavushyan, V.; D'Abrusco, Raffaele; Jiménez-Bailón, E.; La Franca, F.; Paggi, A.; Smith, Howard A.; Tosti, G.
Abstract: The third Fermi source catalog lists 3033 γ -ray sources above 4σ significance. More than 30% are classified as either unidentified/unassociated Gamma-ray sources (UGSs), with about 20% classified as Blazar candidates of uncertain types (BCUs). To confirm the blazar-like nature of candidate counterparts of UGSs and BCUs, we started in 2012 an optical spectroscopic follow up campaign. We report here the spectra of 36 targets with observations from the Observatorio Astronómico Nacional San Pedro Mártir, the Southern Astrophysical Research Observatory, the Kitt Peak National Observatory and the Northern Optical Telescope, between 2016 and 2017. We confirm the BL Lac nature of 23 sources, and the flat spectrum radio quasar nature of other 7 ones. We also provide redshift estimates for 19 out of these 30 confirmations, with only one being a lower limit due to spectral features ascribable to intervening systems along the line of sight. As in previous analyses, the largest fraction of now-classified BCUs belong to the class of BL Lac objects, that appear to be the most elusive class of active galactic nuclei. One of the BL Lacs identified in this work, associated with 3FGL J2213.6-4755, lies at a redshift of z>1.529, making it one of the few distant gamma-ray BL Lac objects.

ID: 155155
Type: article
Authors: Peña-Herazo, H. A.; Massaro, F.; Chavushyan, V.; Marchesini, E. J.; Paggi, A.; Landoni, M.; Masetti, N.; Ricci, F.; D'Abrusco, Raffaele; Milisavljevic, D.; Jiménez-Bailón, E.; La Franca, F.; Smith, Howard A.; Tosti, G.
Abstract: Nearly one third of the sources in the Fermi-LAT catalogs lacks a lower energy counterpart, hence being referred as unidentified/unassociated gamma-ray sources (UGSs). In order to firmly classify them, dedicated multifrequency follow-up campaigns are necessary. These will permit to unveil their nature and identify the fraction that could belong to the class of active galaxies known as blazars that is the largest population of extragalactic γ -ray sources. In Fermi-LAT catalogs there are also gamma-ray sources associated with multifrequency blazar-like objects known as Blazars Candidates of Uncertain type (i.e., BCUs) for which follow up spectroscopic campaigns are mandatory to confirm their blazar nature. Thus, in 2013 we started an optical spectroscopic campaign to identify blazar-like objects potential counterparts of UGSs and BCUs. Here we report the spectra of 31 additional targets observed as part of our follow up campaign. Thirteen of them are BCUs for which we acquired spectroscopic observations at Observatorio Astrofísico Guillermo Haro (OAGH) and at Southern Astrophysical Research Observatory (SOAR) telescopes, while the rest has been identified thanks to the archival observations available from the Sloan Digital Sky Survey (SDSS). We confirm the blazar nature of all BCUs: three of them are in blazar of quasar type (BZQs) while the remaining ones can be spectroscopically classified as BL Lac objects (BZBs). Then we also discovered 18 BL Lac objects lying within the positional uncertainty regions of UGSs that could be their potential counterparts.

ID: 151823
Type: article
Authors: Venhola, Aku; Peletier, Reynier; Laurikainen, Eija; Salo, Heikki; Iodice, Enrichetta; Mieske, Steffen; Hilker, Michael; Wittmann, Carolin; Paolillo, Maurizio; Cantiello, Michele; Janz, Joachim; Spavone, Marilena; D'Abrusco, Raffaele; van de Ven, Glenn; Napolitano, Nicola; Verdoes Kleijn, Gijs; Capaccioli, Massimo; Grado, Aniello; Valentijn, Edwin; Falcón-Barroso, Jesús; Limatola, Luca
Abstract: Context. Dwarf galaxies are the most common type of galaxies in galaxy clusters. Due to their low mass, they are more vulnerable to environmental effects than massive galaxies, and are thus optimal for studying the effects of the environment on galaxy evolution. By comparing the properties of dwarf galaxies with different masses, morphological types, and cluster-centric distances we can obtain information about the physical processes in clusters that play a role in the evolution of these objects and shape their properties. The Fornax Deep Survey Dwarf galaxy Catalog (FDSDC) includes 564 dwarf galaxies in the Fornax cluster and the in-falling Fornax A subgroup. This sample allows us to perform a robust statistical analysis of the structural and stellar population differences in the range of galactic environments within the Fornax cluster.
Aims: By comparing our results with works concerning other clusters and the theoretical knowledge of the environmental processes taking place in galaxy clusters, we aim to understand the main mechanisms transforming galaxies in the Fornax cluster.
Methods: We have exploited the FDSDC to study how the number density of galaxies, galaxy colors and structure change as a function of the cluster-centric distance, used as a proxy for the galactic environment and in-fall time. We also used deprojection methods to transform the observed shape and density distributions of the galaxies into the intrinsic physical values. These measurements are then compared with predictions of simple theoretical models of the effects of harassment and ram pressure stripping on galaxy structure. We used stellar population models to estimate the stellar masses, metallicities and ages of the dwarf galaxies. We compared the properties of the dwarf galaxies in Fornax with those in the other galaxy clusters with different masses.
Results: We present the standard scaling relations for dwarf galaxies, which are the size-luminosity, Sérsic n-magnitude and color-magnitude relations. New in this paper is that we find a different behavior for the bright dwarfs (-18.5 mag _{r' r'} > -16 mag): While considering galaxies in the same magnitude-bins, we find that, while for fainter dwarfs the g'-r' color is redder for lower surface brightness objects (as expected from fading stellar populations), for brighter dwarfs the color is redder for the higher surface brightness and higher Sérsic n objects. The trend of the bright dwarfs might be explained by those galaxies being affected by harassment and by slower quenching of star formation in their inner parts. As the fraction of early-type dwarfs with respect to late-types increases toward the central parts of the cluster, the color-surface brightness trends are also manifested in the cluster-centric trends, confirming that it is indeed the environment that changes the galaxies. We also estimate the strength of the ram-pressure stripping, tidal disruption, and harassment in the Fornax cluster, and find that our observations are consistent with the theoretically expected ranges of galaxy properties where each of those mechanisms dominate. We furthermore find that the luminosity function, color-magnitude relation, and axis-ratio distribution of the dwarfs in the center of the Fornax cluster are similar to those in the center of the Virgo cluster. This indicates that in spite of the fact that the Virgo is six times more massive, their central dwarf galaxy populations appear similar in the relations studied by us.

ID: 150213
Type: article
Authors: Pota, V.; Napolitano, N. R.; Hilker, M.; Spavone, M.; Schulz, C.; Cantiello, M.; Tortora, C.; Iodice, E.; Paolillo, Maurizio; D'Abrusco, Raffaele; Capaccioli, M.; Puzia, T.; Peletier, R. F.; Romanowsky, A. J.; van de Ven, G.; Spiniello, C.; Norris, M.; Lisker, T.; Munoz, R.; Schipani, P.; Eigenthaler, P.; Taylor, M. A.; Sánchez-Janssen, R.; Ordenes-Briceño, Y.
Abstract: We present the results of a wide spectroscopic survey aimed at detecting extragalactic globular clusters (GCs) in the core of the Fornax cluster. About 4500 low-resolution spectra (from 4800 to 10000 Å) were observed in 25 VLT/VIMOS masks covering the central 1 deg² around the dominant galaxy NGC 1399 corresponding to ˜175 kpc galactocentric radius. We describe the methodology used for data reduction and data analysis. We found a total of 387 unique physical objects (372 GCs and 15 ultracompact dwarfs) in the field covered by our observations. Most of these objects lie in the region of NGC 1399 halo, with only 10 per cent likely belonging to other giant galaxies 48 of these objects have a literature counterpart. The new VIMOS data set is complementary to the many GC catalogues already present in the literature and it brings the total number of tracer particles around NGC 1399 to more than 1130 objects. With this comprehensive radial velocity sample, we have found that the velocity dispersion of the GC population (equally for red and blue GC populations) shows a relatively sharp increase from low velocity dispersion ({˜ } 250{-}350 {km s^{-1}}) to high velocity dispersion ({˜ } 300 {-}400 {km s^{-1}}) at projected radius of ≈10 arcmin (˜60 kpc) from the galaxy centre. This suggests that at a projected radius of ≈60 kpc both blue and red GC populations begin to be governed by the dominating Fornax cluster potential, rather than by the central NGC 1399 galaxy potential. This kinematic evidence corroborates similar results found using surface brightness analysis and planetary nebulae kinematics.

ID: 150222
Type: article
Authors: Venhola, Aku; Peletier, Reynier; Laurikainen, Eija; Salo, Heikki; Iodice, Enrichetta; Mieske, Steffen; Hilker, Michael; Wittmann, Carolin; Lisker, Thorsten; Paolillo, Maurizio; Cantiello, Michele; Janz, Joachim; Spavone, Marilena; D'Abrusco, Raffaele; Ven, Glennvande; Napolitano, Nicola; Kleijn, GijsVerdoes; Maddox, Natasha; Capaccioli, Massimo; Grado, Aniello; Valentijn, Edwin; Falcón-Barroso, Jesús; Limatola, Luca
Abstract: Context. The Fornax Deep Survey (FDS), an imaging survey in the u', g', r', and i'-bands, has a supreme resolution and image depth compared to the previous spatially complete Fornax Cluster Catalog (FCC). Our new data allows us to study the galaxies down to r'-band magnitude m_r' ≈ 21 mag (M_r' ≈ -10.5 mag), which opens a new parameter regime to investigate the evolution of dwarf galaxies in the cluster environment. After the Virgo cluster, Fornax is the second nearest galaxy cluster to us, and with its different mass and evolutionary state, it provides a valuable comparison that makes it possible to understand the various evolutionary effects on galaxies and galaxy clusters. These data provide an important legacy dataset to study the Fornax cluster. Aims: We aim to present the Fornax Deep Survey (FDS) dwarf galaxy catalog, focusing on explaining the data reduction and calibrations, assessing the quality of the data, and describing the methods used for defining the cluster memberships and first order morphological classifications for the catalog objects. We also describe the main scientific questions that will be addressed based on the catalog. This catalog will also be invaluable for future follow-up studies of the Fornax cluster dwarf galaxies. Methods: As a first step we used the SExtractor fine-tuned for dwarf galaxy detection, to find galaxies from the FDS data, covering a 26 deg² area of the main cluster up to its virial radius, and the area around the Fornax A substructure. We made 2D-decompositions of the identified galaxies using GALFIT, measure the aperture colors, and the basic morphological parameters like concentration and residual flux fraction. We used color-magnitude, luminosity-radius and luminosity-concentration relations to separate the cluster galaxies from the background galaxies. We then divided the cluster galaxies into early- and late-type galaxies according to their morphology and gave first order morphological classifications using a combination of visual and parametric classifications. Results: Our final catalog includes 14 095 galaxies. We classify 590 galaxies as being likely Fornax cluster galaxies, of which 564 are dwarfs (M_r' > -18.5 mag) consisting our Fornax dwarf catalog. Of the cluster dwarfs we classify 470 as early-types, and 94 as late-type galaxies. Our final catalog reaches its 50% completeness limit at magnitude M_r' = -10.5 mag and surface brightness μ¯_e,r' = 26 mag arcsec^-2, which is approximately three magnitudes deeper than the FCC. Based on previous works and comparison with a spectroscopically confirmed subsample, we estimate that our final Fornax dwarf galaxy catalog has ≲10% contamination from the background objects. The catalogs are only at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/620/A165

ID: 145646
Type: article
Authors: Iodice, E.; Spavone, M.; Cantiello, M.; D'Abrusco, R.; Capaccioli, M.; Hilker, M.; Mieske, S.; Napolitano, N. R.; Peletier, R. F.; Limatola, L.; Grado, A.; Venhola, A.; Paolillo, M.; van de Ven, G.; Schipani, P.
Abstract: In the core of the Fornax cluster, on the west side of NGC 1399, we have detected a previously unknown region of intracluster light (ICL). It is made up by several faint ({μ }_r≃ 28{--}29 mag arcsec^‑2) patches of diffuse light. The bulk of the ICL is located in between the three bright galaxies in the core, NGC 1387, NGC 1379, and NGC 1381, at 10≤slant R≤slant 40 arcmin (∼58–230 kpc) from the central galaxy NGC 1399. We show that the ICL is the counterpart in the diffuse light of the known over-density in the population of blue globular clusters (GCs). The total g-band luminosity of the ICL is {L}_g≃ 8.3× {10}⁹ L _⊙, which is ∼5% of the total luminosity of NGC 1399. This is consistent with the fraction of the blue GCs in the same region of the cluster. The ICL has g-r∼ 0.7 mag, which is similar to the colors in the halo of the bright galaxies in the cluster core. The new findings were compared with theoretical predictions for the ICL formation and they support a scenario in which the intracluster population detected in the core of the Fornax cluster is build up by the tidal stripping of material (stars and GCs) from galaxy outskirts in a close passage with the central brightest galaxy (cD). Moreover, the diffuse form of the ICL and its location close to the core of the cluster is expected in a dynamically evolved cluster like Fornax.