Open AccessA Chandra X‐ray survey of nearby dwarf starburst galaxies – I. Data reduction and results
Author(s) -
Ott Jürgen,
Walter Fabian,
Brinks Elias
Publication year - 2005
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2005.08862.x
Subject(s) - physics , astrophysics , surface brightness , galaxy , luminosity , astronomy , dwarf galaxy , x ray , black body radiation , radiation , quantum mechanics
We present an analysis of Chandra X‐ray observations of a sample of eight dwarf starburst galaxies (I Zw 18, VII Zw 403, NGC 1569, NGC 3077, NGC 4214, NGC 4449, NGC 5253 and He 2–10). Extended, diffuse X‐ray emission is detected in all but two of the objects. Unresolved sources were found within all dwarf galaxies (total: 55 sources). These point sources are well fitted by power‐law (PL), thermal plasma (TP) or blackbody (BB) models. 10 of the point sources exceed an X‐ray luminosity of 10 39 erg s −1 (ultraluminous X‐ray sources, ULXs). In those galaxies where diffuse X‐ray emission is detected, this emission (with X‐ray luminosities ranging from 4 × 10 38 to 2 × 10 40 erg s −1 ) contains most (60–80 per cent) of the X‐ray photons. This diffuse emission can be well fitted by mekal one‐temperature TP models once the contribution from the unresolved point sources is subtracted properly. The diffuse X‐ray component is significantly extended, reaching as far as 0.5–5 kpc into the outskirts of their hosts. Azimuthally averaged X‐ray surface brightness profiles are well approximated by exponential functions. Temperatures of various regions within the galaxies range from 1.6 to 7.6 × 10 6 K . With few exceptions, temperatures of the hot gas are remarkably uniform, hovering around 2–3 × 10 6 K . Temperatures of the coronal gas in the outer regions are in general ∼2–3 times lower than those found in the central regions. Fits to the diffuse emission do not allow strong constraints to be put on the metallicities of the emitting plasmas. However, the derived metallicities are compatible with those determined from their H ii regions. An α/Fe ratio of ∼2 is indicated for the hot gas within at least three objects (NGC 1569, NGC 4449 and He 2–10). Shadowing of the diffuse X‐ray emission by the cooler disc gas is used to constrain the orientation of the galaxies.