A Radio Perspective on the Wet Merger Remnant NGC 34

Abstract

We present Very Large Array observations of the neutral hydrogen and radio continuum of NGC 34 (= NGC 17 = Mrk 938). This object is an ideal candidate for studying the fate of gas in mergers, since, as shown by an optical study done by Schweizer & Seitzer, it is a gas-rich ("wet") merger remnant of two disk galaxies of unequal mass hosting a strong central starburst and a weak active galactic nucleus (AGN). We detect H i emission from both tidal tails and from nearby galaxies, suggesting that NGC 34 is actually part of a gas-rich group and might have recently interacted with one of its companions. The kinematics of the gas suggests this remnant is forming an outer disk of neutral hydrogen from the gas of the northern tail. We also detect broad H i absorption (514 ± 21 km s −1 wide) at both negative and positive velocities with respect to the systemic velocity. This absorption could be explained by the motions of the tidal tails or by the presence of a circumnuclear disk. In addition, we present radio-continuum images that show both nuclear (62.4 ± 0.3 mJy) and extra-nuclear emission (26.5 ± 3.0 mJy). The extra-nuclear component is very diffuse and in the shape of two radio lobes, spanning 390 kpc overall. This emission could be a signature of an AGN that has turned off or it could originate from a starburst-driven superwind. We discuss the possible scenarios that explain our observations, and what they tell us about the location of the gas and the future evolution of NGC 34.

The starburst-active galactic nucleus connection in the merger galaxy Mrk 938: an infrared and X-ray view★

“…This value lies between the values estimated by Vega et al (2008) of 21 and 151 M ⊙ yr −1 based on SED fitting for star formation in the last 10 Myr and averaged over the entire burst, respectively. Also, our derived SFR is similar to the 64 M ⊙ yr −1 obtained from 1.4‐GHz observations (Fernández et al 2010).…”

“…These revealed that the mid‐IR emission in this system originates in the central ∼800 pc (Miles et al 1996), but it actually dominates in a region of ∼400 pc (see discussion in ). Fernández et al (2010) detected H i emission from both tidal tails and from nearby galaxies, suggesting that Mrk 938 is part of a gas‐rich group of galaxies. They also found a hint of emission between Mrk 938 and NGC 35, the largest companion lying at a projected distance of 131 kpc, and suggested that they might have recently interacted.…”

Probing the circumnuclear stellar populations of starburst galaxies in the near-infrared

“…For NGC 34, Fernández et al (2010) calculated the SFR from radio luminosity and found a value of 64 M yr −1 (in a 3 × 2 beam), in agreement with SFR∼50 M yr −1 derived by Prouton et al (2004) from the FIR luminosity for similar beam. For NGC 1614, Alonso-Herrero et al (2001) found SFR=52 M yr −1 from integrated FIR luminosity (in a 45 × 250 beam) and assuming that 70% of this star formation occurs in the nucleus, they predict a nuclear SFR of 36 M yr −1 .…”

GROUND-BASED Paα NARROW-BAND IMAGING OF LOCAL LUMINOUS INFRARED GALAXIES. I. STAR FORMATION RATES AND SURFACE DENSITIES

“…In addition to this structure, we find an extended Paα emission-line region along the southern spiral arm which is located outside the field of view of the HST /NICMOS observation. This galaxy, hosting a strong starburst and a weak AGN, as evidenced by its optical, infrared, radio, and X-ray properties, is known as a remnant of unequal gas-rich merger (e.g., Fernández et al 2010;Schweizer & Seitzer 2007). It is an S0/a (HyperLeda) and classified as a Seyfert 2 by a long-slit spectroscopic study (Veilleux et al 1995).…”