arXiv:astro-ph/0511516v1 17 Nov 2005 DRAFT VERSION MAY 27, 2019 Preprint typeset using L A T E X style emulateapj v. 11/12/01 A SPECTACULAR X-RAY STRIPPING TAIL IN THE CLUSTER A3627 M. SUN, 1 C. J ONES, 2 W. FORMAN, 2 P. E. J. NULSEN, 2,3 M. DONAHUE, 1 M. VOIT 1 1) Department of Physics and Astronomy, MSU, East Lansing, MI 48824; sunm@pa.msu.edu 2) Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 3) University of Wollongong, NSW 2522, Australia, on leave Draft version May 27, 2019 ABSTRACT We present the discovery of a straight and narrow 70 kpc X-ray tail from the small late-type galaxy ESO 137- 001 in the nearby, hot (T=6.5 keV) merging cluster A3627, from both Chandra and XMM-Newton observations. The tail has a length-to-width ratio of ∼ 10 and almost all the X-ray emission is outside ESO 137-001. The X-ray tail is luminous (L 0.5−2keV ∼ 10 41 ergs s −1 ), with a temperature of ∼ 0.7 keV and a total X-ray gas mass of ∼ 10 9 M ⊙ (∼ 10% of the galaxy’s stellar mass). We interpret this tail as the stripped interstellar medium of ESO 137-001 mixed with the hot cluster medium. The straightness and narrowness of the tail implies that the ICM turbulence is not strong on scales of 20 - 70 kpc. Subject headings: galaxies: clusters: general — galaxies: clusters: individual (A3627) — X-rays: galaxies — galaxies: individual (ESO 137-001) 1. INTRODUCTION The intracluster medium (ICM) has long been proposed to play a vital role in shaping the properties of cluster galaxies, especially through stripping the cold galactic materials. Ram- pressure stripping is likely an important factor for galaxy trans- formation in rich environments (e.g., Quilis, Moore & Bower 2000). Radio observations have long revealed an HI deficiency in cluster galaxies, which is a strong indication of stripping (e.g., Giovanelli & Haynes 1985). In X-rays, the first galaxy to show a significant stripping tail is M86 in Virgo (Forman et al. 1979), while more and more cases of stripping have been revealed by the Chandra and XMM-Newton data (e.g., Wang et al. 2004; Sun & Vikhlinin 2005, SV05 hereafter; Machacek et al. 2005a,b). Recently we carried out a systematic analy- sis of X-ray thermal coronae of ∼ 160 galaxies in 21 nearby (z < 0.04) hot (kT > 3 keV) clusters (Sun et al. in prep.). During our analysis, we found a narrow tailed X-ray source in A3627, which is apparently associated with a late-type galaxy ESO 137-001. The narrowness and length of the tail makes it the most dramatic X-ray stripping tail of a galaxy to date. A3627 is a nearby massive galaxy cluster in the core of the Great Attractor. Kraan-Korteweg et al. (1996) found, through a deep imaging and spectroscopic survey for galaxies behind the Milky Way, that A3627 (at a Galactic latitude of -7.2 ◦ ) is an extremely rich cluster rivaling Coma and Perseus in mass and galactic content. A major cluster merger is implied by the ear- lier X-ray observations from the ROSAT and ASCA that reveal the elongation of the cluster in the southeast - northwest direc- tion (Fig. 1a) and a temperature gradient (5 - 8 keV) along the same direction (Bohringer et al. 1996; Tamura et al. 1998). The velocity of ESO 137-001 is 4630 ± 58 km/s, almost the same velocity as A3627, 4707 km/s (NASA/IPAC Extragalac- tic Database - NED). In this paper, we adopt the redshift of the cluster to calculate the distance of ESO 137-001. Assuming H 0 = 70 km s −1 Mpc −1 , Ω M =0.3, and Ω Λ =0.7, the luminosity dis- tance is 68.2 Mpc, and 1 ′′ =0.321 kpc. Uncertainties quoted in this paper are 1 σ . 2. Chandra AND XMM-Newton DATA The tailed X-ray source is on one (ObsID 4956) of our three 15 ks Chandra pointings on A3627, performed with the Ad- vanced CCD Imaging Spectrometer (ACIS) in June 14 - 15, 2004. No background flares are detected. Standard data anal- ysis has been performed which includes the corrections for the slow gain change and the ACIS low energy quantum efficiency degradation. The calibration files used correspond to Chandra Calibration Database 3.1.0 from the Chandra X-ray Center. The source also is in an 18 ks XMM-Newton observation. Pipeline products provided by the XMM-Newton Science Op- erations Center, consisting of calibrated event files, were used in this analysis. Both PN and MOS data have been reduced with the Science Analysis Software (SAS) 6.5.0. After remov- ing large background flares, 17.8 ks, 18.0 ks and 12.1 ks clean exposure are left for MOS1, MOS2 and PN respectively. SAS tools ARFGEN and RMFGEN were used to produce the re- sponse files. 3. THE TAILED X- RAY SOURCE The XMM-Newton photon image and the adaptively smoothed Chandra images are shown in Fig. 1b, c and d. An X-ray source with a long narrow tail is significant. The tailed source is only visible in the soft X-ray images. The brighter southeast end of the source is on a known cluster galaxy ESO 137-001 (Fig. 1c). There are no other galaxies as bright as ESO 137-001 in the B band within 7 ′ of ESO 137- 001 in the direction of the tail. Thus, we conclude the X-ray extended source is the stripped tail of ESO 137-001. ESO 137-001 is in a very crowded field with many Galactic stars, which may affect the results of ground-based photomet- ric measurements. The galaxy is bright in the optical B band, but faint on the 2MASS Ks band. The B band luminosity is 2.3-4.0×10 10 L ⊙ from NED and LEDA, depending on the cor- rection of the internal extinction. The Ks band luminosity is 1.4×10 10 L ⊙ . Assuming a Ks band mass-to-light ratio of 0.73 M ⊙ /L ⊙ (Cole et al. 2001), the total stellar mass of ESO 137- 001 is only 1.1×10 10 M ⊙ , which makes it ∼ 5 times less mas- sive than a L ∗ galaxy. The B-Ks color of ESO 137-001 is 1.0- 1.6, much smaller than the B-Ks color of a typical early-type or late-type galaxy (3.7-4.0 or ∼ 3, Jarrett 2000). Thus, ESO 137- 1