XMM‐NewtonObservations of NGC 507: Supersolar Metal Abundances in the Hot Interstellar Medium

Abstract

We present the results of the X-ray XMM-Newton observations of NGC 507, a dominant elliptical galaxy in a small group of galaxies, and report supersolar metal abundances of both Fe and -elements in the hot interstellar medium (ISM) of this galaxy. These results are robust in that we considered all possible systematic effects in our analysis. We find Z Fe ¼ 2 3 times solar inside the D 25 ellipse of NGC 507. This is the highest Z Fe reported so far for the hot halo of an elliptical galaxy; this high iron abundance is fully consistent with the predictions of stellar evolution models, which include the yield of both Type II and Type Ia supernovae (SNe). Our analysis shows that abundance measurements are critically dependent on the selection of the proper emission model. The spatially resolved, high-quality XMM-Newton spectra provide enough statistics to formally require at least three emission components in each of four circumnuclear concentric shells (within 5 0 or 100 kpc): two soft thermal components indicating a range of temperatures in the hot ISM plus a harder component, consistent with the integrated output of low-mass X-ray binaries (LMXBs) in NGC 507. The two-component (thermal+LMXB) model customarily used in past studies yields a much lower Z Fe , consistent with previous reports of subsolar metal abundances. This model, however, gives a significantly worse fit to the data (F-test probability < 0:0001). The abundance of -elements (most accurately determined by Si) is also found to be supersolar. The -element-to-Fe abundance ratio is close to the solar ratio, suggesting that $70% of the iron mass in the hot ISM originated from Type Ia SNe. The -element-to-Fe abundance ratio remains constant out to at least 100 kpc, indicating that Types II and Ia SN ejecta are well mixed on a scale much larger than the extent of the stellar body.

Chemical Enrichment of the Complex Hot ISM of the Antennae Galaxies. I. Spatial and Spectral Analysis of the Diffuse X‐Ray Emission

“…This conclusion also agrees with unrelated recent results that demonstrate how fitting thermal plasmas with simplified (singletemperature) emission models may underestimate metal abundances (e.g., Molendi & Gastaldello 2001;Kim & Fabbiano 2004;see Fabbiano 1995 andBuote &Fabian 1998 for earlier discussions of this effect).…”

On the Anomalous Temperature Distribution of the Intergalactic Medium in the NGC 3411 Group of Galaxies

“…There will be some powerlaw contribution from X-ray binaries within NGC 3411; from the L X; dscr -L K relation of Kim & Fabbiano (2004a) we expect L X;dscr ¼ 5:1 AE 2:0 ; 10 40 ergs s À1 . In both XMM-Newton and Chandra data the addition of power-law component produces only a small improvement in the fit.…”

Time‐dependent Circulation Flows: Iron Enrichment in Cooling Flows with Heated Return Flows

“…A common feature of well-studied X-ray-luminous galaxy groups is an extended region of enhanced iron emission surrounding the central elliptical galaxy (e.g., Buote et al 2003aBuote et al , 2003bSun et al 2003;Xue et al 2004;Kim & Fabbiano 2004). Typically, the iron abundance is near solar within 30-40 kpc of the center and decreases outward within 100-150 kpc.…”

“…While we have used the NGC 5044 group in our discussion, the same argument could be applied to many other similar galaxy groups and poor clusters with kT $ 1 keV: RGH 80 ( Xue et al 2004), NGC 507 ( Kim & Fabbiano 2004), MKW 4 (O'Sullivan et al 2003, and NGC 1399 (Buote 2000a(Buote , 2000b. In every case the hot gas surrounding the central elliptical has an extended region that can be fitted better with more than one local temperature and is enriched to hz Fe i$ 0:5 solar out to k50 kpc by the products of SNeIa.…”