2,100 research outputs found
Discovery of two infrared supernovae: a new window on the SN search
We report the discovery of two supernovae (SN 1999gw and SN 2001db) obtained
within the framework of an infrared monitoring campaign of Luminous Infrared
Galaxies, aimed at detecting obscured supernovae. SN 2001db, extinguished by
Av~5.5 mag, is the first supernova discovered in the infrared which has
received the spectroscopic confirmation. This result highlights the power of
infrared monitoring in detecting obscured SNe and indicates that optical
surveys are probably missing a significant fraction of SNe, especially in
obscured systems such as starburst galaxies. The preliminary estimate of SN
rate in LIRG galaxies is about an order of magnitude higher than that expected
from optical surveys.Comment: 9 pages, 7 figures, accepted for publication in A&
A search for changing-look AGN in the Grossan catalog
We observed with XMM-Newton 4 objects selected from the Grossan catalog, with
the aim to search for new 'changing-look' AGN. The sample includes all the
sources which showed in subsequent observations a flux much lower than the one
measured with HEAO A-1: NGC 7674, NGC 4968, IRAS 13218+0552 and NGC 1667. None
of the sources was caught in a high flux state during the XMM-Newton
observations, whose analysis reveal they are all likely Compton-thick objects.
We suggest that, for all the sources, potential problems with the HEAO A-1
source identification and flux measurement prevent us from being certain that
the HEAO A-1 data represent a putative 'high' state for these objects.
Nonetheless, based on the high flux state and Compton-thin spectrum of its
GINGA observation, NGC 7674 represents probably the sixth known case of a
'changing-look' Seyfert 2 galaxy. From the X-ray variability pattern, we can
estimate a likely lower limit of a few parsec to the distance of the inner
walls of the torus in this object. Remarkably, IRAS 13218+0552 was not detected
by XMM-Newton, despite being currently classified as a Seyfert 1 with a large
[OIII] flux. However, the original classification was likely to be affected by
an extreme velocity outflow component in the emission lines. The object likely
harbors an highly obscured AGN and should be re-classified as a Type 2 source.Comment: 11 pages, 12 figures, accepted for publication in A&
Strong [CII] emission at high redshift
We report the detection of the [CII]157.74um fine-structure line in the
lensed galaxy BRI 0952-0115 at z=4.43, using the APEX telescope. This is the
first detection of the [CII] line in a source with L_FIR < 10^13 L_sun at high
redshift. The line is very strong compared to previous [CII] detections at
high-z (a factor of 5-8 higher in flux), partly due to the lensing
amplification. The L_[CII]/L_FIR ratio is 10^-2.9, which is higher than
observed in local galaxies with similar infrared luminosities. Together with
previous observations of [CII] at high redshift, our result suggests that the
[CII] emission in high redshift galaxies is enhanced relative to local galaxies
of the same infrared luminosity. This finding may result from selection effects
of the few current observations of [CII] at high redshift, and in particular
the fact that non detections may have not been published (although the few
published upper limits are still consistent with the [CII] enhancement
scenario). If the trend is confirmed with larger samples, it would indicate
that high-z galaxies are characterized by different physical conditions with
respect to their local counterparts. Regardless of the physical origin of the
trend, this effect would increase the potential of the [CII]158um line to
search and characterize high-z sources.Comment: Accepted for publication in A&A Letters, 5 pages, 2 figure
- …