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An X-Ray View of 82 Liners with Chandra and XMM-Newton Data O

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An X-Ray View of 82 Liners with Chandra and XMM-Newton Data O CORE Metadata, citation and similar papers at core.ac.uk Provided by Digital.CSIC Astronomy & Astrophysics manuscript no. O.Gonzalez-Martin-LINERs˙xray c ESO 2009 May 13, 2009 An X-ray view of 82 LINERs with Chandra and XMM-Newton data O. Gonzalez-Mart´ ´ın1 ;?, J. Masegosa2, I. Marquez´ 2, M. Guainazzi3 and E. Jimenez-Bail´ on´ 4 1 X-ray Astronomy Group, Department of Physics and Astronomy, Leicester University, Leicester LE1 7RH, UK e-mail: [email protected] 2 Instituto de Astrof´ısica de Andaluc´ıa, CSIC, Granada, SPAIN 3 European Space Astronomy Centre of ESA, P.O. Box 78, Villanueva de la Canada, E-28691 Madrid, SPAIN 4 Instituto de Astronom´ıa, Universidad Nacional Autonoma´ de Mexico, Apartado Postal 70-264, 04510 Mexico DF, MEXICO ABSTRACT We present the results of an homogeneous X-ray analysis for 82 nearby LINERs selected from the catalogue of Carrillo et al. (1999). All sources have available Chandra (68 sources) and/or XMM-Newton (55 sources) observations. This is the largest sample of LINERs with X-ray spectral data (60 out of the 82 objects) and significantly improves our previous analysis based on Chandra data for 51 LINERs (Gonzalez-Martin et al. 2006). It increases both the sample size and adds XMM-Newton data. New models permit the inclusion of double absorbers in the spectral fits. Nuclear X-ray morphology is inferred from the compactness of detected nuclear sources in the hard band (4.5-8.0 keV). Sixty per cent of the sample shows a compact nuclear source and are classified as AGN candidates. The spectral analysis indicates that best fits involve a composite model: absorbed primary continuum and (2) soft spectrum below 2 keV described by an absorbed scatterer and/or a thermal component. The resulting median spectral parameters and their standard deviations are: < Γ >=2.11 0.52 , < kT >=0.54 0.30 keV, < log(NH1) >=21.32 0.71 and < log(NH2) >=21.93 1.36 . We complement our X-ray results with our analysis of HST optical images and literature data on emission lines, radio compactness and stellar population. Adding all these multiwavelength data, we conclude that evidence do exist supporting the AGN nature of their nuclear engine for 80% of the sample (66 out of 82 objects). Key words. Galaxies – Active Nuclei – X-rays – Catalogs 1. Introduction inated by emission lines of moderate intensities arising from gas in lower ionisation states than classical AGN. Previous studies The term Active Galactic Nucleus (AGN) generally refers to the of LINERs reached different conclusions about the ionisation galaxies that show energetic phenomena in their nuclei which mechanism responsible for the LINER emission. Possibilities cannot be unambiguously attributed to starlight. The 2-10 keV included: 1) shock heating (Dopita and Sutherland, 1995), 2) X-ray luminosity has been used as a reasonably reliable mea- Wolf-Rayet or OB stars in compact near-nuclear star clusters sure of AGN power allowing one to extract information about (Terlevich and Melnick, 1985; Filippenko and Terlevich, 1992) the central engine from the spectral fit and to quantify the ab- 24 −2 and 3) low luminosity AGN (Ho et al., 1997; Eracleous and sorbing material (NH < 1:5 × 10 cm from current missions), Halpern, 2001). i.e. the dusty torus. Nearby examples of both Seyfert 2 (Maiolino et al., 1998; Risaliti et al., 1999; Page et al., 2003; Cappi et al., 2006; Panessa et al., 2006), and Seyfert 1 (Nandra et al., 2007) or It is therefore important to isolate and study the nature of the PG-QSOs (Piconcelli et al., 2005; Jimenez-Bailon et al., 2005) source hosted by most of the LINERs. Satyapal et al. (2005) (see have been studied. The X-ray regime can also be used to search also Ho et al., 2001; Satyapal et al., 2004; Dudik et al., 2005) for AGN in heavily obscured objects. This is important for high estimated 2-10 keV luminosities for a sample of 41 LINERs redshift surveys (Comastri and Brusa, 2008) and starburst sam- using Chandra data. They found that AGN are very frequent ples (Tzanavaris and Georgantopoulos, 2007). among LINERs. Eddington ratio considerations led them to con- These studies are especially important for low luminosity clude that LINERs represent the faint end of the fundamen- 44 −1 AGN (LLAGN) with bolometric luminosities LB < 10 erg s tal correlation between mass accretion and star formation rates because more than 40% of nearby galaxies show evidence for (e.g. LINERs very inefficient accreting systems). Flohic et al. low-power AGN (see the review by Ho, 2008). Even at lower (2006) studied a sample of 19 LINERs using archival Chandra luminosities Zhang et al. (2009) have recently studied the X-ray data and found that the median AGN contribution to the 0.5– nuclear activity of 187 nearby galaxies, most of them classed 10 keV luminosity is 60%). They suggest that AGN power is as non-active, with Chandra data, finding evidences for AGN not sufficient to produce the observed optical emission lines and in 46% of their sample (60 % when considering ellipticals and invoke shocks and/or stellar processes. Our previous analysis early-type spirals). (Gonzalez-Martin et al., 2006b, hereinafter GM+06) presented We focused our attention on low ionisation narrow emission- results from an homogeneous analysis of 51 LINER galaxies ob- line regions (LINERs), originally defined as a subclass of served with Chandra. Morphological classification together with LLAGN by Heckman (1980). They show optical spectra dom- spectral analysis (when possible) led us to conclude that at least 60% of LINERs may host an AGN. Following Ho et al. (1997), ? E-mail: [email protected] (University of Leicester); we consider a LINER to host an AGN when the nuclear regions [email protected] (IAA) showing an unresolved source at high X-ray energies. 2 O. Gonzalez-Martin et al.: An X-ray view of 82 LINERs 1.00 1.00 (a) (a) 0.75 0.75 0.50 0.50 0.25 0.25 Norm. Distrib. 0.00 Norm. Distrib. 0.00 0.00 0.02 0.04 0.06 0.08 0.10 0.00 0.02 0.04 0.06 0.08 0.10 Redshift Redshift 1.00 1.00 (b) (b) 0.75 0.75 0.50 0.50 0.25 0.25 Norm. Distrib. 0.00 Norm. Distrib. 0.00 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 Morph. type Morph. type 1.00 1.00 (c) (c) 0.75 0.75 0.50 0.50 0.25 0.25 Norm. Distrib. 0.00 Norm. Distrib. 0.00 -23 -22 -21 -20 -19 -18 -17 -16 -15 -23 -22 -21 -20 -19 -18 -17 -16 -15 Absolute Magnitude Absolute Magnitude 1.00 1.00 (d) (d) 0.75 0.75 0.50 0.50 0.25 0.25 Norm. Distrib. 0.00 Norm. Distrib. 0.00 8 9 10 11 12 13 14 15 16 17 18 19 8 9 10 11 12 13 14 15 16 17 18 19 Apparent Magnitude Apparent Magnitude Fig. 1. (Left): total sample of LINERs in MCL (empty histogram) versus X-ray sample (dashed histogram), normalised to the peak. (Right): X-ray sample (empty histogram) versus the sample reported by GM+06, normalised to the peak. (a) Redshift, (b) morphological types (from the RC3 catalog: t<0 are for ellipticals, t=0 for S0, t=1 for Sa, t=3 for Sb, t=5 for Sc, t=7 for Sd, and t>8 for irregulars), (c) absolute magnitudes, and (d) apparent magnitudes distributions. This paper presents a study of 82 LINERs which is the 2. The sample and the data largest sample so far analyzed at X-ray wavelengths. In con- trast to GM+06 we include objects observed with XMM-Newton Our sample was extracted from the multi-wavelength LINER 1 yielding 68 sources with Chandra and 55 with XMM-Newton catalogue compiled by Carrillo et al. (1999) (hereinafter MCL ). data. The high spatial resolution of the Chandra optics is op- We updated the sample by including all the galaxies in MCL timally suited to disentangle the different components of the with available Chandra data up to 2007-06-30 and XMM- often complex X-ray morphology (GM+06) found in our sam- Newton data up to 2007-04-30. We recall that only Chandra ple. Analysis of X-ray images is improved by using a different data were used in GM+06. The search has been done using 2 smoothing process. On the other hand, the addition of XMM- the HEASARC archive. The sample includes 108 LINERs with Newton data complements Chandra by allowing more detailed Chandra data and 107 LINERs with XMM-Newton data. Seventy spectral analysis in 60 of the sources. In contrast to GM+06, six objects are present in both archives yielding a total of 139 we now use a different baseline model with the main improve- LINERs. ment being the use of an additional power-law component and LINER identifications were revised using standard diagnos- two neutral absorbers. We present a detailed study of the X- tic diagrams (Baldwin et al., 1981; Veilleux and Osterbrock, ray LINER properties added to multiwavelength information. 1987). We obtained emission line fluxes for all but 18 ob- In summary, compared to GM+06, the current paper presents jects from the literature (Ho et al., 2001; Veilleux et al., 1995; 33 new LINERs, 19 new Chandra data, presents XMM-Newton Moustakas and Kennicutt, 2006; Wu et al., 1998).
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