679 research outputs found
Angular motion of a PAH molecule in interstellar environment
Polycyclic aromatic hydrocarbon (PAH) molecules have recently been proposed as an important and hitherto undetected component of the Interstellar Medium (ISM). The theory was based on an explanation of the Unidentified IR Emission Bands by Leger et al. It has already led to a verified prediction on extended galactic and extragalactic emissions measured by IRAS, or by a recent balloon borne experiment. The physics that rules the motion of such molecules in the ISM was studied, taking into account their coupling with the ambient gas, the radiation field (absorption and emission) and the static magnetic field. This is important for many implications of the PAH theory such as the radio emission by these molecules or the expected polarization of their IR emission. A reflection nebulae is considered where the situation is rather well known. Every day life of a mean PAH molecule in such a region is as follows: every 3 hrs a UV photon is absorbed heating the molecule to a thousand degs; the temperature decay due to cooling by IR emission follows then within a few seconds. A collision with a molecule of gas occurs typically once a week, while an H atom is ejected or captured at the same rate. A typical cooling cycle after a heat impulse is given. The PAH molecules studied as representative of the family has typically 50 atoms, a radius of 4.5 A, is circular and has a molecular mass of M = 300; its permanent dipole moment is 3 Debye
The Canada-France High-z Quasar Survey: 1.2mm Observations
We report 250 GHz (1.2 mm) observations of a sample of 20 QSOs at redshifts
5.8<z<6.5 from the the Canada-France High-z Quasar Survey (CFHQS), using the
Max-Planck Millimeter Bolometer (MAMBO) array at the IRAM 30-metre telescope. A
rms sensitivity <~ 0.6 mJy was achieved for 65% of the sample, and <~ 1.0 mJy
for 90%. Only one QSO, CFHQS J142952+544717, was robustly detected with
S_250GHz = 3.46 +/-0.52 mJy. This indicates that one of the most powerful known
starbursts at z~6 is associated with this radio loud QSO. On average, the other
CFHQS QSOs, which have a mean optical magnitude fainter than previously studied
SDSS samples of z~6 QSOs, have a mean 1.2 mm flux density = 0.41
+/-0.14 mJy; such a 2.9-sigma average detection is hardly meaningful. It would
correspond to ~ 0.94+/-0.32 10^12 Lo, and an average star formation
rate of a few 100's Mo/yr, depending on the IMF and a possible AGN contribution
to . This is consistent with previous findings of Wang et al. (2011) on
the far-infrared emission of z~6 QSOs and extends them toward optically fainter
sources.Comment: 6 pages, 1 figure, A&A in pres
Extinctions at 7um and 15um from the ISOGAL survey
The extinction laws at 7um and 15um are derived for more than 120 sightlines
in the inner Galactic plane based on the ISOGAL survey data and the
near-infrared data from DENIS and 2MASS. The tracers are the ISOGAL point
sources with [7]-[15]<0.4 which are RGB tip stars or early AGB stars with
moderate mass loss. They have well-defined intrinsic color indices (J-Ks)_0,
(Ks-[7])_0 and (Ks-[15])_0. By a linear fitting of the observed color indices
Ks-[7] and Ks-[15] to the observed J-Ks, we obtain the ratio between the
E(Ks-[7]) and E(Ks-[15]) color excesses and E(J-Ks). We infer the selective
extinctions at 7 and 15um in terms of the near-infrared extinction in the Ks
band. The distribution of the derived extinctions around 7 micron (A_7) is well
represented by a Gaussian function, with the peak at about 0.47A_Ks and ranging
from 0.33 to 0.55A_Ks (using the near-infrared extinctions of Rieke & Lebovsky
1985). There is some evidence that A_7/A_Ks may vary significantly depending on
the line of sight. The derived selective extinction at 15um suffers uncertainty
mainly from the dispersion in the intrinsic color index (Ks-[15])_0 which is
affected by dust emission from mass-losing AGB stars. The peak value of A_15 is
around 0.40A_Ks.Comment: 21 pages, 6 figures, accepted for publication in Astronomy and
Astrophysic
The sub-millimeter properties of broad absorption line quasars
We have carried out the first systematic survey of the sub-millimeter
properties of broad absorption line (BAL) quasars. 30 BAL quasars drawn from a
homogeneously selected sample from the Sloan Digital Sky Survey at redshifts
2<z<2.6 were observed with the SCUBA array at the JCMT to a typical rms
sensitivity of 2.5 mJy. Eight quasars were detected at > 2 sigma significance,
four of which are at > 3 sigma significance. The far-infrared luminosities of
these quasars are > 10^{13} L_solar. There is no correlation of sub-millimeter
flux with either the strength of the broad absorption feature or with absolute
magnitude in our sample. We compare the sub-millimeter flux distribution of the
BAL quasar sample with that of a sample of quasars which do not show BAL
features in their optical spectra and find that the two are indistinguishable.
BAL quasars do not have higher sub-millimeter luminosities than non-BAL
quasars. These findings are consistent with the hypothesis that all quasars
would contain a BAL if viewed along a certain line-of-sight. The data are
inconsistent with a model in which the BAL phenomenon indicates a special
evolutionary stage which co-incides with a large dust mass in the host galaxy
and a high sub-millimeter luminosity. Our work provides constraints on
alternative evolutionary explanations of BAL quasars.Comment: 8 pages, 2 figures, ApJ, in pres
86 GHz SiO maser survey of late-type stars in the Inner Galaxy. IV. SiO emission and infrared data for sources in the Scutum and Sagittarius-Carina arms, 20 deg < l < 50 deg
We present an 86 GHz SiO (v = 1, J = 2 ---> 1) maser search toward late-type
stars located within |b|<0.5 deg and 20 deg < l < 50 deg. This search is an
extension at longer longitudes of a previously published work. We selected 135
stars from the MSX catalog using color and flux criteria and detected 92 (86
new detections). The detection rate is 68%, the same as in our previous study.
The last few decades have seen the publication of several catalogs of point
sources detected in infrared surveys (MSX, 2MASS, DENIS, ISOGAL, WISE, GLIMPSE,
AKARI, and MIPSGAL). We searched each catalog for data on the 444 targets of
our earlier survey and for the 135 in the survey reported here. We confirm
that, as anticipated, most of our targets have colors typical of oxygen-rich
asymptotic giant branch (AGB) stars. Only one target star may have already left
the AGB. Ten stars have colors typical of carbon-rich stars, meaning a
contamination of our sample with carbon stars <=1.7%.Comment: 13 pages, 6 Figures, A&A accepte
Detection of CO (2-1) and Radio Continuum Emission from the z = 4.4 QSO BRI 1335-0417
We have detected redshifted CO (2-1) emission at 43 GHz and radio continuum
emission at 1.47 and 4.86 GHz from the z = 4.4 QSO BRI 1335-0417 using the Very
Large Array. The CO data imply optically thick emission from warm (>30 K)
molecular gas with a total mass, M(H_2), of 1.5+/-0.3 x10^{11} M_solar, using
the Galactic gas mass-to-CO luminosity conversion factor. We set an upper limit
to the CO source size of 1.1", and a lower limit of 0.23"x(T_ex/50K)^{-1/2},
where T_ex is the gas excitation temperature. We derive an upper limit to the
dynamical mass of 2x10^{10} x sin^{-2} i M_solar, where i is the disk
inclination angle. To reconcile the gas mass with the dynamical mass requires
either a nearly face-on disk (i < 25deg), or a gas mass-to-CO luminosity
conversion factor significantly lower than the Galactic value. The spectral
energy distribution from the radio to the rest-frame infrared of BRI 1335-0417
is consistent with that expected from a nuclear starburst galaxy, with an
implied massive star formation rate of 2300+/-600 M_solar yr^{-1}.Comment: standard AAS LATEX forma
Experimental verification of minima in excited long-range Rydberg states of Rb_2
Recent theoretical studies with alkali atoms A excited to high
Rydberg states predicted the existence of ultra long-range molecular bound
states. Such excited dimers have large electric dipole moments which, in
combination with their long radiative lifetimes, make them excellent candidates
for manipulation in applications. This letter reports on experimental
investigations of the self-broadening of Rb principal series lines, which
revealed multiple satellites in the line wings. The positions of the satellites
agree quantitatively with theoretically-predicted minima in the excited
long-range Rydberg states of Rb.Comment: 3 figures, 5 pages in two-column forma
Observation of H_2O in a strongly lensed Herschel-ATLAS source at z = 2.3
The Herschel survey, H-ATLAS, with its large areal coverage, has recently discovered a number of bright, strongly lensed high-z submillimeter galaxies. The strong magnification makes it possible to study molecular species other than CO, which are otherwise difficult to observe in high-z galaxies. Among the lensed galaxies already identified by H-ATLAS, the source J090302.9-014127B (SDP.17b) at z = 2.305 is remarkable because of its excitation conditions and a tentative detection of the H_2O 2_(02)-1_(11) emission line (Lupu et al. 2010, ApJ, submitted). We report observations of this line in SDP.17b using the IRAM interferometer equipped with its new 277â371âGHz receivers. The H_2O line is detected at a redshift of z = 2.3049 ± 0.0006, with a flux of 7.8 ± 0.5 Jy km s^(-1) and a FWHM of 250 ± 60 â km â s^(-1). The new flux is 2.4 times weaker than the previous tentative detection, although both remain marginally consistent within 1.6Ï. The intrinsic line luminosity and ratio of H_2O(2_(02) â 1_(11))/CO(8 â 7) are comparable with those of the nearby starburst/enshrouded-AGN Mrk 231, and the ratio I(H_2O)/L_(FIR) is even higher, suggesting that SDP.17b could also host a luminous AGN. The detection of a strong H_2O 2_(02) â 1_(11) line in SDP.17b implies an efficient excitation mechanism of the water levels that must occur in very dense and warm interstellar gas probably similar to Mrk 231
Recent star formation in the inner Galactic Bulge seen by ISOGAL. I - Classification of bright mid-IR sources in a test field
Context: The stellar populations in the central region of the Galaxy are
poorly known because of the high visual extinction and very great source
density in this direction.
Aims: To use recent infrared surveys for studying the dusty stellar objects
in this region.
Methods: We analyse the content of a 20x20 arcmin^2 field centred at
(l,b)=(-0.27,-0.06) observed at 7 and 15 microns as part of the ISOGAL survey.
These ISO observations are more than an order of magnitude better in
sensitivity and spatial resolution than the IRAS observations. The sources are
cross-associated with other catalogues to identify various types of objects. We
then derive criteria to distinguish young objects from post-main sequence
stars.
Results: We find that a sample of about 50 young stellar objects and
ultra-compact HII regions emerges, out of a population of evolved AGB stars. We
demonstrate that the sources colours and spatial extents, as they appear in the
ISOGAL catalogue, possibly complemented with MSX photometry at 21 microns, can
be used to determine whether the ISOGAL sources brighter than 300 mJy at 15
microns (or [15] < 4.5 mag) are young objects or late-type evolved stars.Comment: 15 pages, 12 figures. Accepted for publication in Astronomy and
Astrophysic
- âŠ