Article

Investigating the nuclear activity of barred spiral galaxies: the case of NGC 1672

The Astrophysical Journal (Impact Factor: 6.73). 04/2011; 734. DOI: 10.1088/0004-637X/734/1/33
Source: arXiv

ABSTRACT We have performed an X-ray study of the nearby barred spiral galaxy NGC1672,
primarily to ascertain the effect of the bar on its nuclear activity. We use
both Chandra and XMM-Newton observations to investigate its X-ray properties,
together with supporting high-resolution optical imaging data from the Hubble
Space Telescope (HST), infrared imaging from the Spitzer Space Telescope, and
ATCA ground-based radio data. We detect 28 X-ray sources within the D25 area of
the galaxy, many of which correlate spatially with star-formation in the bar
and spiral arms, while two are identified as background galaxies in the HST
images. Nine of the X-ray sources are ULXs, with the three brightest (LX > 5E39
erg/s) located at the ends of the bar. With the spatial resolution of Chandra,
we are able to show for the first time that NGC1672 possesses a hard
(Gamma~1.5) nuclear X-ray source with a 2-10 keV luminosity of 4E38 erg/s. This
is surrounded by an X-ray bright circumnuclear star-forming ring, comprised of
point sources and hot gas, which dominates the 2-10 keV emission in the central
region of the galaxy. The spatially resolved multiwavelength photometry
indicates that the nuclear source is a low-luminosity AGN (LLAGN), but with
star formation activity close to the central black hole. A high-resolution
multiwavelength survey is required to fully assess the impact of both
large-scale bars and smaller-scale phenomena such as nuclear bars, rings and
nuclear spirals on the fueling of LLAGN.

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    ABSTRACT: Based on a homogeneous set of X-ray, infrared and ultraviolet observations from Chandra, Spitzer, GALEX and 2MASS archives, we study populations of high-mass X-ray binaries (HMXBs) in a sample of 29 nearby star-forming galaxies and their relation with the star formation rate (SFR). In agreement with previous results, we find that HMXBs are a good tracer of the recent star formation activity in the host galaxy and their collective luminosity and number scale with the SFR, in particular, Lx~2.6 10^{39} SFR. However, the scaling relations still bear a rather large dispersion of ~0.4 dex, which we believe is of a physical origin. We present the catalog of 1057 X-ray sources detected within the $D25$ ellipse for galaxies of our sample and construct the average X-ray luminosity function (XLF) of HMXBs with substantially improved statistical accuracy and better control of systematic effects than achieved in previous studies. The XLF follows a power law with slope of 1.6 in the logLx~35-40 luminosity range with a moderately significant evidence for a break or cut-off at Lx~10^{40} erg/s. As before, we did not find any features at the Eddington limit for a neutron star or a stellar mass black hole. We discuss implications of our results for the theory of binary evolution. In particular we estimate the fraction of compact objects that once upon their lifetime experienced an X-ray active phase powered by accretion from a high mass companion and obtain a rather large number, fx~0.2 (0.1 Myr/tau_x) (tau_x is the life time of the X-ray active phase). This is ~4 orders of magnitude more frequent than in LMXBs. We also derive constrains on the mass distribution of the secondary star in HMXBs.
    Monthly Notices of the Royal Astronomical Society 05/2011; 419(3). · 5.52 Impact Factor

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