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ALABAMA University Libraries THE UNIVERSITY OF ALABAMA University Libraries Elemental Abundancies in the X-ray Gas of Early-type Galaxies with XMM-Newton and Chandra Observations Jimmy A. Irwin – University of Michigan et al. Deposited 09/13/2018 Citation of published version: Ji, J., et al. (2009): Elemental Abundancies in the X-ray Gas of Early-type Galaxies with XMM-Newton and Chandra Observations. The Astrophysical Journal, 696(2). http://dx.doi.org/10.1088/0004-637X/696/2/2252 © 2009. The American Astronomical Society. All rights reserved. Printed in the U.S.A. The Astrophysical Journal, 696:2252–2268, 2009 May 10 doi:10.1088/0004-637X/696/2/2252 C 2009. The American Astronomical Society. All rights reserved. Printed in the U.S.A. ELEMENTAL ABUNDANCES IN THE X-RAY GAS OF EARLY-TYPE GALAXIES WITH XMM-NEWTON AND CHANDRA OBSERVATIONS Jun Ji, Jimmy A. Irwin, Alex Athey, Joel N. Bregman, and Edward J. Lloyd-Davies Department of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA; [email protected], [email protected], [email protected], [email protected], [email protected] Received 2008 June 13; accepted 2009 February 23; published 2009 April 29 ABSTRACT The source of hot gas in elliptical galaxies is thought to be due to stellar mass loss, with contributions from supernova (SN) events and possibly from infall from a surrounding environment. This picture predicts supersolar values for the metallicity of the gas toward the inner part of the galaxy, which can be tested by measuring the gas phase abundances. We use high-quality data for 10 nearby early-type galaxy from XMM-Newton, featuring both the European Photon Imaging Camera and the Reflection Grating Spectrometer, where the strongest emission lines are detected with little blending; some Chandra data are also used. We find excellent consistency in the elemental abundances between the different XMM-Newton instruments and good consistency with Chandra. Differences in abundances with aperture size and model complexity are examined, but large differences rarely occur. For a two- temperature thermal model plus a point source contribution, the median Fe and O abundances are 0.86 and 0.44 of the solar value, while Si and Mg abundances are similar to that for Fe. This is similar to stellar abundances for these galaxies but SNe were expected to enhance the gas phase abundances considerably, which is not observed. Key words: cooling flows – galaxies: abundances – galaxies: elliptical and lenticular, cD – galaxies: individual (NGC 720, NGC 1399, NGC 3923, NGC 4406, NGC 4472, NGC 4553, NGC 4636, NGC 4649, NGC 5044, IC 1459) – X-rays: galaxies Online-only material: color figures 1. INTRODUCTION can vary within a galaxy, so by analyzing projected emission, there are multiple temperature components. Also, there are point Early-type galaxies possess an interstellar medium that is sources, mainly due to low-mass X-ray binaries, and these pro- dominated by hot gas (3–10 × 106 K), although the mass of gas vide a hard continuum that must be accounted for. Even with can vary widely between systems. The origin of the hot gas is not Chandra, not all of the individual point sources can be excluded, entirely a settled issue, but it is probably the result of mass loss although their collective spectra are fairly constant from galaxy from stars within the galaxy as well as infall onto the galaxy, to galaxy (Irwin et al. 2003), so modeling of this component especially when it lies in a galaxy group. The abundances of is tractable. Spectrally, one could identify the need for various this gas reflect its history and can potentially inform us as to spectral components if it were possible to measure lines of vari- the number of Type I and Type II supernovae (SNe) that must ous ionization states for the same element. ROSAT did not have have been present. There have been a number of surprises in the sufficient spectral resolution nor bandpass coverage to constrain abundance measurements, such as that the abundance is lower many of the important parameters, nor did it have the spatial than initially predicted for gas shed from stars and enhanced resolution to remove point sources. The ASCA satellite could by SNe (e.g., Arimoto et al. 1997). Also, the values for the measure the high energy contribution from the X-ray binaries, gas abundances have varied considerably, for different models but had very poor spatial resolution and there were calibration applied to the same galaxy, and between galaxies, so a uniform issues at the important low-energy part of the detector. picture has been slow to emerge. Some of these issues are resolved by using Chandra and There are a variety of issues that face investigators when XMM-Newton observations. The Chandra data have excellent determining abundances within early-type galaxies (or other spatial resolution, so most point sources can be excluded, and systems with thermal gas). There is the problem of instrumental the combination of spectral resolution and calibration is superior calibration, which can be notoriously difficult, despite dedicated to its predecessors. In comparison, XMM-Newton has poorer efforts by the scientific staff. It is often several years after launch spatial resolution but more collecting area and a relatively of a mission before most of the important calibration issues are high dispersion grating spectrum is obtained for all on-axis understood. As the calibrations for XMM-Newton and Chandra targets. have matured, this is a good time to examine the spectra of There is a range of results that seems puzzling, as both high similar objects and compare the results. and low metallicities are found in optically similar galaxies. Another issue is that the derived metallicities are sensitive Individual XMM-Newton observations show a similar range of to the number of spectral components used in a model. This behavior, with subsolar abundances (referenced to Anders & was pointed out by Trinchieri et al. (1994), among others, who Grevesse 1989), as in NGC 6251 (Sambruna et al. 2004), NGC showed that when a single-temperature thermal model was ap- 3585, 4494, and 5322 (O’Sullivan & Ponman 2004), near-solar plied to the luminous emission from an elliptical galaxy, the values, as in NGC 4649 (Randall et al. 2006), through the derived metallicity was significantly lower than when a two- supersolar values seen in NGC 507 (Kim & Fabbiano 2004). temperature (2T) model was used. Often, the χ 2 is acceptable Similarly, individual Chandra observations of galaxies can be for both models, so without further information, it is difficult of near solar metallicity, such as in NGC 1316 (Kim & Fabbiano to identify the correct model. The problem is one of resolution, 2003) or NGC 4649 (Randall et al. 2004), but other galaxies can both spatially and spectrally. On the one hand, the temperature show quite low abundances, such as NGC 1291 (Irwin et al. 2252 No. 2, 2009 ABUNDANCES IN X-RAY EARLY-TYPE GALAXIES 2253 Table 1 Properties and Observational Information of Surveyed Galaxies a 0 b c d e f g Galaxy Type BT D NH re ObsID Net Exposure Time (ks) (mag) (Mpc) (1020 cm−2) (arcsec) MOS1 MOS2 PN RGS1 RGS2 ACIS-S NGC 720 E5 11.13 27.67 1.55 39.87 0112300101 29.6 30.0 19.9 46.3 45.3 ··· NGC 1399 cD;E1pec 10.44 19.95 1.31 42.55 0400620101 121.5 120.5 73.9 118.2 118.1 ··· NGC 1399 ··· ··· ··· ··· ··· 319h - ··· ··· ··· ··· 55.9 NGC 3923 E4-5 10.62 22.91 6.29 53.35 0027340101 38.8 38.7 29.8 43.9 42.6 ··· NGC 4406 S0(3)/E3 9.74 17.14 2.58 89.64 0108260201 77.9 78.9 47.8 83.5 81.1 ··· NGC 4472 E2/S0 9.33 16.29 1.65 104.40 0200130101 82.5 82.7 72.8 101.5 101.5 ··· NGC 4472 ··· ··· ··· ··· ··· 321h - ··· ··· ··· ··· 32.5 NGC 4552 E 10.57 15.35 2.56 48.89 0141570101 27.8 31.2 18.5 42.9 42.8 ··· NGC 4636 E/S0_1 10.43 14.66 1.83 100.08 0111190701 59.2 59.3 51.1 62.9 61.4 ··· NGC 4649 E2 9.70 16.83 2.13 73.73 0021540201 50.6 50.6 42.2 53.1 51.6 ··· NGC 4649 ··· ··· ··· ··· ··· 785h - ··· ··· ··· ··· 22.9 NGC 5044 E0 11.67 31.19 5.03 82.23 0037950101 22.6 22.7 17.0 23.6 22.8 ··· IC 1459 E3 10.83 29.24 1.19 38.61 0135980201 29.3 29.3 25.2 31.7 30.8 ··· Notes. a The galaxy type was take from NED. b Total B-band magnitude from RC3 (De Vaucouleurs et al. 1991). c Distances in Mpc, measured by a surface brightness fluctuation method (Tonry et al. 2001). d The Galactic H i column density, taken from the dust map by Dickey & Lockman (1990). e Effective, blue-half light radius in arcseconds derived from RC3 (De Vaucouleurs et al. 1991). f XMM-Newton observation ID. g Net exposure time after filtering background flares. h Chandra ObsID. 2002). Two surveys of galaxies with Chandra also show a range in their sample which were observed by XMM-Newton, and are metallicities, but with no meaningful correlation between the bright enough to use both of the data of the European Photon stellar metallicities and the metallicities of the X-ray emitting Imaging Camera (EPIC) and the Reflection Grating Spectrom- gas (Athey 2007; Humphrey & Buote 2006). eter (RGS). This is mainly determined by the quality of the If there is a consistent trend, it is with the ratios of some RGS spectra, which were included in our sample by presenting of the elements, such as in the XMM-Newton observation of enough emission line features in the preview spectra.
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