140 research outputs found
Molecules in galaxies
The main achievements, current developments and prospects of molecular
studies in external galaxies are reviewed. They are put in the context of the
results of several decades of studies of molecules in local interstellar
medium, their chemistry and their importance for star formation. CO
observations have revealed the gross structure of molecular gas in galaxies.
Together with other molecules, they are among the best tracers of star
formation at galactic scales. Our knowledge about molecular abundances in
various local galactic environments is progressing. They trace physical
conditions and metallicity, and they are closely related to dust processes and
large aromatic molecules. Major recent developments include mega-masers, and
molecules in Active Galactic Nuclei; millimetre emission of molecules at very
high redshift; and infrared H2 emission as tracer of warm molecular gas, shocks
and photodissociation regions. The advent of sensitive giant interferometers
from the centimetre to sub-millimetre range, especially ALMA in the near future
in the mm/submm range, will open a new area for molecular studies in galaxies
and their use to trace star formation at all distances.Comment: 96 pages, 11 figure
Star formation rate and dynamical mass of 10^8 solar mass black hole host galaxies at redshift 6
We present ALMA observations of two moderate luminosity quasars at redshift
6. These quasars from the Canada-France High-z Quasar Survey (CFHQS) have black
hole masses of ~10^8 M_solar. Both quasars are detected in the [CII] line and
dust continuum. Combining these data with our previous study of two similar
CFHQS quasars we investigate the population properties. We show that z>6
quasars have a significantly lower far-infrared luminosity than
bolometric-luminosity-matched samples at lower redshift, inferring a lower star
formation rate, possibly correlated with the lower black hole masses at z=6.
The ratios of [CII] to far-infrared luminosities in the CFHQS quasars are
comparable with those of starbursts of similar star formation rate in the local
universe. We determine values of velocity dispersion and dynamical mass for the
quasar host galaxies based on the [CII] data. We find that there is no
significant offset from the relations defined by nearby galaxies with similar
black hole masses. There is however a marked increase in the scatter at z=6,
beyond the large observational uncertainties.Comment: 10 pages, 7 figures, accepted for publication in Ap
Interstellar Fullerene Compounds and Diffuse Interstellar Bands
Recently, the presence of fullerenes in the interstellar medium (ISM) has
been confirmed especially with the first confirmed identification of two strong
diffuse interstellar bands (DIBs) with C60+. This justifies reassesing the
importance of interstellar fullerenes of various sizes with endohedral or
exohedral inclusions and heterofullerenes (EEHFs). The phenomenology of
fullerenes is complex. In addition to fullerene formation in shock shattering,
fully dehydrogenated PAHs in diffuse interstellar (IS) clouds could perhaps
efficiently transform into fullerenes including EEHFs. But it is extremely
difficult to assess their expected abundance, composition and size
distribution, except for C60+. EEHFs share many properties with C60, as regards
stability, formation/destruction and chemical processes, and many basic
spectral features. We address the interstellar importance of various EEHFs as
possible DIB carriers. Specifically, we discuss IS properties and the
contributions of fullerenes of various sizes and charge such as C60+,
metallofullerenes, heterofullerenes, fulleranes, fullerene-PAH compounds,
H2@C60. We conclude that the landscape of interstellar fullerenes is probably
much richer than heretofore realized. EEHFs, together with pure fullerenes of
various sizes, have properties necessary to be suitably carriers of DIBs:
carbonaceous nature; stability and resilience in the ISM; various heteroatoms
and ionization states; relatively easy formation; few stable isomers; right
spectral range; energy internal conversion; Jahn-Teller fine structure. This is
supported by the C60+ DIBs. But, the lack of information about optical spectra
other than C60 and IS abundances still precludes definitive assessment of the
importance of fullerenes as DIB carriers. Their compounds could significantly
contribute to DIBs, but it still seems difficult that they are the only
important DIB carriers.Comment: 29 pages, 6 figures, revised as published in Astronomy and
Astrophysic
A wide dispersion in star formation rate and dynamical mass of 10^8 solar mass black hole host galaxies at redshift 6
ALMA [CII] line and continuum observations of five redshift z>6 quasars are
presented. This sample was selected to probe lower black hole mass quasars than
most previous studies. We find a wide dispersion in properties with CFHQS
J0216-0455, a low-luminosity quasar with absolute magnitude M_1450=-22.2,
remaining undetected implying a limit on the star formation rate in the host
galaxy of <10 solar masses per year, whereas other host galaxies have star
formation rates up to hundreds of solar masses per year. Two other quasars have
particularly interesting properties. VIMOS2911 is one of the least luminous z>6
quasars known with M_1450=-23.1, yet its host galaxy is experiencing a very
powerful starburst. PSO J167-13 has a broad and luminous [CII] line and a
neighbouring galaxy a projected distance of 5kpc away that is also detected in
the [CII] line and continuum. Combining with similar observations from the
literature, we study the ratio of [CII] line to far-infrared luminosity finding
this ratio increases at high-redshift at a fixed far-infrared luminosity,
likely due to lower dust content, lower metallicity and/or higher gas masses.
We compile a sample of 21 high-redshift quasars with dynamical masses and
investigate the relationship between black hole mass and dynamical mass. The
new observations presented here reveal dynamical masses consistent with the
relationship defined by local galaxies. However, the full sample shows a very
wide scatter across the black hole mass - dynamical mass plane, whereas both
the local relationship and simulations of high-redshift quasars show a much
lower dispersion in dynamical mass.Comment: 10 pages, 11 figures, ApJ in pres
CO Emission from z>3 Radio Galaxies
We report on the detection of the CO(4-3) line with the IRAM Plateau de Bure
Interferometer in two z>3 radio galaxies, doubling the number of successful
detections in such objects. A comparison of the CO and Ly-alpha velocity
profiles indicates that in at least half of the cases, the CO is coincident in
velocity with associated HI absorption seen against the Ly-alpha emission. This
strongly suggests that the CO and HI originate from the same gas reservoir, and
could explain the observed redshift differences between the optical narrow
emission lines and the CO. The CO emission traces a mass of H_2 100-1000 times
larger than the HI and HII mass traced by Ly-alpha, providing sufficient gas to
supply the massive starbursts suggested by their strong thermal dust emission.Comment: 6 Pages, including 3 PostScript figures. To appear in the proceedings
of the conference "Radio Galaxies: Past, present and future", Leiden, 11-15
Nov 2002, eds. M. Jarvis et a
Redshift 6.4 host galaxies of 10^8 solar mass black holes: low star formation rate and dynamical mass
We present ALMA observations of rest-frame far-infrared continuum and [CII]
line emission in two z=6.4 quasars with black hole masses of ~10^8 M_sun. CFHQS
J0210-0456 is detected in the continuum with a 1.2 mm flux of 120+/-35 microJy,
whereas CFHQS J2329-0301 is undetected at a similar noise level. J2329-0301 has
a star formation rate limit of <40 M_sun/yr, considerably below the typical
value at all redshifts for this bolometric luminosity. By comparison with hydro
simulations, we speculate that this quasar is observed at a relatively rare
phase where quasar feedback has effectively shut down star formation in the
host galaxy. [CII] emission is also detected only in J0210-0456. The ratio of
[CII] to far-infrared luminosity is similar to that of low redshift galaxies of
comparable luminosity, suggesting the previous finding of an offset in the
relationships between this ratio and far-infrared luminosity at low- and
high-redshift may be partially due to a selection effect from the limited
sensitivity of previous observations. The [CII] line of J0210-0456 is
relatively narrow (FWHM=189+/-18 km/s), indicating a dynamical mass
substantially lower than expected from the local black hole - velocity
dispersion correlation. The [CII] line is marginally resolved at 0.7"
resolution with the blue and red wings spatially offset by 0.5" (3 kpc) and a
smooth velocity gradient of 100 km/s across a scale of 6 kpc, possibly due to
rotation of a galaxy-wide disk. These observations are consistent with the idea
that stellar mass growth lags black hole accretion for quasars at this epoch
with respect to more recent times.Comment: 8 pages, 7 figures, ApJ in press, replaced with final versio
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
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