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A radio study of the superwind galaxy NGC1482

We present multifrequency radio continuum as well as HI observations of the superwind galaxy NGC1482, with both the GMRT and the VLA. This galaxy has a remarkable hourglass-shaped optical emission line outflow as well as bi-polar soft X-ray bubbles on oppo

a r X i v :a s t r o -p h /0411628v 1 23 N o v 2004Mon.Not.R.Astron.Soc.000,1–??()Printed 2February 2008(MN L A T E X style ?le v1.4)

A radio study of the superwind galaxy NGC 1482Ananda Hota 1,2?and D.J.Saikia 2?

1

Joint Astronomy Programme,Indian Institute of Science,Bangalore 560012,India 2National Centre for Radio Astrophysics,TIFR,Pune University Campus,Post Bag 3,Pune 411007,India Accepted.Received ABSTRACT We present multifrequency radio continuum as well as H i observations of the super-wind galaxy NGC1482,with both the Giant Metrewave Radio Telescope (GMRT)and the Very Large Array (VLA).This galaxy has a remarkable hourglass-shaped optical emission line out?ow as well as bi-polar soft X-ray bubbles on opposite sides of the galactic disk.The low-frequency,lower-resolution radio observations show a smooth structure.From the non-thermal emission,we estimate the available energy in super-novae,and examine whether this would be adequate to drive the observed superwind out?ow.The high-frequency,high-resolution radio images of the central starburst re-gion located at the base of the superwind bi-cone shows one prominent peak and more extended emission with substructure.This image has been compared with the infrared,optical red-continuum,H α,and,soft and hard X-ray images from Chandra to understand the nature and relationship of the various features seen at di?erent wavelengths.The peak of infrared emission is the only feature which is coincident with the prominent radio peak,and possibly de?nes the centre of the galaxy.The H i observations with the GMRT show two blobs of emission on opposite sides of the central region.These are rotating about the centre of the galaxy and are located at ?2.4kpc from it.In addition,these observations also reveal a multicomponent H i -absorption pro?le against the central region of the radio source,with a total width of ?250km s ?1.The extreme blue-and red-shifted absorption components are at 1688and 1942km s ?1respectively,while the peak absorption is at 1836km s ?1.This is consistent with the heliocentric systemic velocity of 1850±20km s ?1,estimated from a variety of observations.We discuss possible implications of these results.Key words:galaxies:individual (NGC1482)–galaxies:active –galaxies:starburst –galaxies:kinematics and dynamics –radio continuum:galaxies –radio lines:galaxies

1INTRODUCTION

Galactic-scale out?ows along the minor-axes of nearby edge-

on galaxies have been observed over a wide frequency range

extending from radio continuum to X-ray wavelengths.The

more prominent out?ows with an out?ow mass and kinetic

energy of approximately 105?107M ⊙and 1053?1055

ergs respectively are often referred to as superwinds,and

these have been observed over a wide range of redshifts (e.g.

Heckman,Armus &Miley 1990;Pettini et al.2001;Veilleux

2002a,2003).The superwind could contain di?erent phases

of the metal enriched interstellar medium (ISM)such as hot

X-ray emitting gas,warm ionized gas emitting ultraviolet

(UV)and optical emission lines,synchrotron emitting rel-

ativistic plasma and magnetic ?elds,dust,as well as H i ?hota@ncra.tifr.res.in ?djs@ncra.tifr.res.in

and molecular gas (Dahlem 1997;Strickland 2001).These superwinds play an important role in heating and supply-ing kinetic energy to the Inter Galactic Medium (IGM)and enriching it with metals.Many of these out?ows are inter-preted as the combined e?ect of numerous supernovae and stellar winds in the nuclear starforming region of the par-ent Seyfert or starburst galaxy.An active galactic nucleus (AGN)or winds from the tori in the nuclear regions could also contribute to the observed out?ows (Heckman et al.1990;Balsara &Krolik 1993;Baum et al.1993;Krolik &Kriss 1995;Colbert et al.1996a,b;Weaver 2001;Veilleux 2002b).In this paper we present a detailed radio study of

the interesting superwind galaxy NGC1482,which has re-

ceived relatively little attention.The basic properties of this

galaxy are summarised in Table 1.In an emission-line sur-

vey of early-type spirals Hameed &Devereux (1999)no-

ticed the presence of “?laments and/or chimneys of ionized c RAS

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