A. Ruiz

Publications (4)0 Total impact

• Article: Analysis of Spitzer-IRS spectra of hyperluminous infrared galaxies

  A. Ruiz, G. Risaliti, E. Nardini, F. Panessa, F. J. Carrera
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  ABSTRACT: Hyperluminous infrared galaxies (HLIRG) are the most luminous persistent objects in the Universe. They exhibit extremely high star formation rates, and most of them seem to harbour an AGN. They are unique laboratories to investigate the most extreme star formation, and its connection to super-massive black hole growth. The AGN and SB relative contributions to the total output in these objects is still debated. Our aim is to disentangle the AGN and SB emission of a sample of thirteen HLIRG. We have studied the MIR low resolution spectra of a sample of thirteen HLIRG obtained with the IRS on board Spitzer. The 5-8 {\mu}m range is an optimal window to detect AGN activity even in a heavily obscured environment. We performed a SB/AGN decomposition of the continuum using templates, successfully applied for ULIRG in previous works. The MIR spectra of all sources is largely dominated by AGN emission. Converting the 6 {\mu}m luminosity into IR luminosity, we found that ~80% of the sample shows an IR output dominated by the AGN emission. However, the SB activity is significant in all sources (mean SB contribution ~30%), showing star formation rates ~300-3000 solar masses per year. Using X-ray and MIR data we estimated the dust covering factor (CF) of these HLIRG, finding that a significant fraction presents a CF consistent with unity. Along with the high X-ray absorption shown by these sources, this suggests that large amounts of dust and gas enshroud the nucleus of these HLIRG, as also observed in ULIRG. Our results are in agreement with previous studies of the IR SED of HLIRG using radiative transfer models, and we find strong evidence that all HLIRG harbour an AGN. This work provides further support to the idea that AGN and SB are both crucial to understand the properties of HLIRG. Our study of the CF supports the hypothesis that HLIRG can be divided in two different populations.
  10/2012;
• Source

  Available from: Francisco J. Carrera

  Article: Spectral Energy Distribution of Hyper-Luminous Infrared Galaxies

  A. Ruiz, G. Miniutti, F. Panessa, F. J. Carrera
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  ABSTRACT: The relationship between star formation and super-massive black hole growth is central to our understanding of galaxy formation and evolution. Hyper-Luminous Infrared Galaxies (HLIRGs) are unique laboratories to investigate the connection between starburst (SB) and Active Galactic Nuclei (AGN), since they exhibit extreme star formation rates, and most of them show evidence of harbouring powerful AGN. Our previous X-ray study of a sample of 14 HLIRGs shows that the X-ray emission of most HLIRGs is dominated by AGN activity. To improve our estimate of the relative contribution of the AGN and SB emission to its total bolometric output, we have built broad band spectral energy distributions (SEDs) for these HLIRGs, and we have fitted empirical AGN and SB templates to these SEDs. In broad terms, most sources are well fitted using this method, and we found AGN and SB contributions similar to those obtained by previous studies of HLIRGs. We have classified the HLIRGs SEDs in two groups, named class A and class B. Class A HLIRGs show a flat SED from the optical to the infrared energy range. Three out of seven class A sources can be modelled with a pure luminosity-dependent QSO template, while the rest of them require a type 1 AGN template and a SB template. The SB component is dominant in three out of four class A objects. Class B HLIRGs show SEDs with a prominent and broad IR bump. These sources can not trivially be modelled with a combination of pure AGN and pure SB, they require templates of composite objects, suggesting that >50% of their emission comes from stellar formation processes. We propose that our sample is actually composed by three different populations: very luminous QSO, young galaxies going through their maximal star formation period and the high luminosity tail of ULIRG population distribution. Comment: 22 pages, 26 figures, accepted for publication in Astronomy & Astrophysics
  03/2010;
• Source

  Available from: Francisco J. Carrera

  Article: An XMM-Newton study of Hyper-Luminous Infrared Galaxies

  A. Ruiz, F. J. Carrera, F. Panessa
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  ABSTRACT: Hyper-Luminous Infrared Galaxies (HLIRGs) are the most luminous persistent objects in the Universe. They exhibit extremely high star formation rates, and most of them seem to harbour an AGN. They are unique laboratories to investigate utmost star formation, and its connection to super-massive black hole growth. X-ray studies of HLIRGs have the potential to unravel the AGN contribution to the bolometric output from these bright objects. We have selected a sample of 14 HLIRGs observed by XMM-Newton (type 1, type 2 AGN and starburst), 5 of which are candidates to be Compton-thick objects. This is the first time that a systematic study of this type of objects is carried out in the X-ray spectral band. Their X-ray spectral properties have been correlated with their IR luminosities, estimated by IRAS, ISO and sub-mm data. The X-ray spectra of HLIRGs present heterogeneous properties. All our X-ray detected HLIRGs (10) have AGN-dominated X-ray spectra. The hard X-ray luminosity of 8 of them is consistent with a pure AGN contribution, while in the remaining 2 sources both an AGN and a starburst seem to contribute to the overall emission. We found soft excess emission in 5 sources. In one of them it is consistent with a pure starburst origin, while in the other 4 sources it is consistent with an AGN origin. The observed X-ray emission is systematically below the one expected for a standard local QSO of the same IR luminosity, suggesting the possible presence of absorption in type 2 objects and/or a departure from a standard spectral energy distribution of QSO. The X-ray-to-IR-luminosity ratio is constant with redshift, indicating similar evolutions for the AGN and starburst component, and that their respective power sources could be physically related.
  06/2007;
• Article: Spectral energy distribution of hyperluminous infrared galaxies

  A. Ruiz, G. Miniutti, F. Panessa, F. J. Carrera
  http://dx.doi.org/10.1051/0004-6361/200912235.