arXiv subjects

B. Balmaverde

Publications and source records attributed to B. Balmaverde.

42 records · Page 3Linked to original sources

arXiv2012

Multi-band constraints on the nature of emission line galaxies

Our aim is to explore the nature of emission line galaxies by combining high-resolution observations obtained in different bands to understand which objects are powered by an Active Galactic Nucleus(AGN). From the spectroscopic Palomar survey of nearby bright galaxies, we selected a sample of 18 objects observed with HST, Chandra, and VLA. No connection is found between X-ray and emission line luminosities from ground-based data, unlike what is found for brighter AGN. Conversely, a strong correlation emerges when using the HST spectroscopic data, which are extracted on a much smaller aperture. This suggests that the HST data better isolate the AGN component when one is present, while ground-based line measurements are affected by diffuse emission from the host galaxies. The sample separates into two populations. The 11 objects belonging to the first class have an equivalent width of the [OIII] emission line measured from HST data EW([OIII])>~2 A and are associated with an X-ray nuclear source; in the second group we find seven galaxies with EW([OIII])<~1 A that generally do not show any emission related to an active nucleus (emission lines, X-ray, or radio sources). This latter group includes about half of the Low Ionization Nuclear Emission-line region (LINERs) or transition galaxies of the sample, all of which are objects of low [OIII] line luminosity (<~1E38 erg s-1) and low equivalent width (<~1 A) in ground-based observations. These results strengthen the suggestion that the EW([OIII]) value is a robust predictor of the nature of an emission line galaxy.

astro-ph.CO↗

arXiv2012

Chandra Observations of 3C Radio Sources with z<0.3 II: completing the snapshot survey

We report on the second round of Chandra observations of the 3C snapshot survey developed to observe the complete sample of 3C radio sources with z<0.3 for 8 ksec each. In the first paper, we illustrated the basic data reduction and analysis procedures performed for the 30 sources of the 3C sample observed during the Chandra Cycle 9, while here, we present the data for the remaining 27 sources observed during Cycle 12. We measured the X-ray intensity of the nuclei and of any radio hotspots and jet features with associated X-ray emission. X-ray fluxes in three energy bands: soft, medium and hard for all the sources analyzed are also reported. For the stronger nuclei, we also applied the standard spectral analysis which provides the best fit values of X-ray spectral index and absorbing column density. In addition, a detailed analysis of bright X-ray nuclei that could be affected by pileup has been performed. X-ray emission was detected for all the nuclei of the radio sources in our sample except for 3C 319. Amongst the current sample, there are two compact steep spectrum radio sources; two broad line radio galaxies; and one wide angle tail radio galaxy, 3C 89, hosted in a cluster of galaxies clearly visible in our Chandra snapshot observation. In addition, we also detected soft X-ray emission arising from the galaxy cluster surrounding 3C 196.1. Finally, X-ray emission from hotspots have been found in three FR II radio sources and, in the case of 3C 459, we also report the detection of X-ray emission associated with the eastern radio lobe and as well as that cospatial with radio jets in 3C 29 and 3C 402.

astro-ph.HE↗

arXiv2012

Extended soft X-ray emission in 3CR radio galaxies at z < 0.3: High Excitation and Broad Line Galaxies

We analyze Chandra observations of diffuse soft X-ray emission associated with a complete sample of 3CR radio galaxies at z < 0.3. In this paper we focus on the properties of the spectroscopic sub-classes of high excitation galaxies (HEGs) and broad line objects (BLOs). Among the 33 HEGs we detect extended (or possibly extended) emission in about 40% of the sources; the fraction is even higher (8/10) restricting the analysis to the objects with exposure times larger than 10 ks. In the 18 BLOs, extended emission is seen only in 2 objects; this lower detection rate can be ascribed to the presence of their bright X-ray nuclei that easily outshine any genuine diffuse emission. A very close correspondence between the soft X-ray and optical line morphology emerges. We also find that the ratio between [O III] and extended soft X-ray luminosity is confined within a factor of 2 around a median value of 5. Both results are similar to what is seen in Seyfert galaxies. We discuss different processes that could explain the soft X-ray emission and conclude that the photoionization of extended gas, coincident with the narrow line region, is the favored mechanism.

astro-ph.CO↗

arXiv2012

Examining the Radio-Loud/Radio-Quiet dichotomy with new Chandra and VLA observations of 13 UGC galaxies

(Abridged) We present the results from new 15 ks Chandra-ACIS and 4.9 GHz Very Large Array observations of 13 galaxies hosting low luminosity AGN. This completes the multiwavelength study of a sample of 51 nearby early-type galaxies described in Capetti & Balmaverde (2005, 2006); Balmaverde & Capetti (2006). The aim of the three previous papers was to explore the connection between the host galaxies and AGN activity in a radio-selected sample. We detect nuclear X-ray emission in eight sources and radio emission in all but one (viz., UGC6985). The new VLA observations improve the spatial resolution by a factor of ten: the presence of nuclear radio sources in 12 of the 13 galaxies confirms their AGN nature. As previously indicated, the behavior of the X-ray and radio emission in these sources depends strongly on the form of their optical surface brightness profiles derived from Hubble Space Telescope imaging, i.e., on their classification as "core", "power-law" or "intermediate" galaxies. With more than twice the number of "power-law" and "intermediate" galaxies compared to previous work, we confirm with a much higher statistical significance that these galaxies lie well above the radio-X-ray correlation established in FRI radio galaxies and the low-luminosity "core" galaxies. This result highlights the fact that the "radio-loud/radio-quiet" dichotomy is a function of the host galaxy's optical surface brightness profile. We present radio-optical-X-ray spectral indices for all 51 sample galaxies. Survival statistics point to significant differences in the radio-to-optical and radio-to-X-ray spectral indices between the "core" and "power-law" galaxies (Gehan's Generalized Wilcoxon test probability "p" for the two classes being statistically similar is <10^-5), but not in the optical-to-X-ray spectral indices (p=0.25).

astro-ph.CO↗

arXiv2006

The Chandra view of the 3C/FRI sample of low luminosity radio-galaxies

We present results from Chandra observations of the 3C/FRI sample of low luminosity radio-galaxies. We detected a power-law nuclear component in 12 objects out of the 18 with available data. In 4 galaxies we detected nuclear X-ray absorption at a level of about N_H= (0.2-6)e22 cm-2. X-ray absorbed sources are associated with the presence of highly inclined dusty disks (or dust filaments projected onto the nuclei) seen in the HST images. This suggests the existence of a flattened X-ray absorber, but of much lower optical depth than in classical obscuring tori. We thus have an un-obstructed view toward most FR~I nuclei while absorption plays only a marginal role in the remaining objects. Three pieces of evidence support an interpretation for a jet origin for the X-ray cores: i) the presence of strong correlations between the nuclear luminosities in the radio, optical and X-ray bands, extending over 4 orders of magnitude and with a much smaller dispersion (about 0.3 dex) when compared to similar trends found for other classes of AGNs, pointing to a common origin for the emission in the three bands; ii) the close similarity of the broad-band spectral indices with the sub-class of BL Lac objects sharing the same range of extended radio-luminosity, in accord with the FRI/BL Lacs unified model; iii) the presence of a common luminosity evolution of spectral indices in both FRI and BL Lacs. The low luminosities of the X-ray nuclei, regardless of their origin, strengthens the interpretation of low efficiency accretion in low luminosity radio-galaxies.

astro-ph↗

arXiv2005

The host galaxy/AGN connection in nearby early-type galaxies. Is there a miniature radio-galaxy in every "core" galaxy?

This is the second of a series of three papers exploring the connection between the multiwavelength properties of AGN in nearby early-type galaxies and the characteristics of their hosts. In Capetti et al. (2005) we presented a study of the surface brightness profiles for the 65 objects with available archival HST images out of the 116 radio-detected galaxies. We classified early-type galaxies into ``core'' and ``power-law'' galaxies, discriminating on the basis of the slope of their nuclear brightness profiles. Here we focus on the 29 core galaxies (hereafter CoreG). We used HST and Chandra data to isolate their nuclear emission. The CoreG invariably host radio-loud nuclei, with an average radio-loudness parameter of Log R = 3.6. The optical and X-ray nuclear luminosities correlate with the radio-core power, smoothly extending the analogous correlations already found for low luminosity radio-galaxies. This supports the interpretation of a common non-thermal origin of the nuclear emission also for CoreG. The luminosities of the nuclear sources, most likely dominated by jet emission, set firm upper limits, as low as L/L_Edd = 10^{-9} in both the optical and X-ray band, on any emission from the accretion process. The similarity of CoreG and LLRG indicates that they are drawn from the same population of early-type galaxies. LLRG represent only the tip of the iceberg associated with (relatively) high activity levels, with CoreG forming the bulk of the population. A minimum black hole mass of M_{BH} = 10^8 M_sun is apparently associated with the radio-loud nuclei in both CoreG and LLRG, but this effect must be tested on a sample of less luminous galaxies, likely to host smaller black holes. ABRIDGED.

astro-ph↗