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STAR FORMATION IN
GALAXIES FROM IRAS DATA NEW HSB GALAXIES, ARAKELIAN GALAXIES, KARACHENTSEV GALAXIES, MARKARIAN GALAXIES 1.STAR
BURST ACTIVITY IN HIGH SURFACE
BRIGHTNESS GALAXIES Petrov (1986) published a list of 47 new high surface brightness galaxies (HSBGs) in the Nilson (1973) system of diameters i. e. with surface brightness B < 22mp/sqr.arcsec , where B is defined by B = mp - 0.25
cosec | bII|+ 2.5 log [3.14(Dxd)/4] + 0.22D/d + 0.73 . Petrov (1986) showed
that Nilson's system of diameters
presents a more stringent criterion for HSBGs than
Arakelians one (1975) - only 24% of all
193 Arakelian galaxies included in the UCGC are HSBGs in the Nilson
system. IRAS data were used to make a general study of the star burst activity in this type of galaxies. It conforms with the theoretical statements of Desert (1986) that the IR fluxes in the HSBGs are due to higher star burst activity. The main conclusions are: a) More than 50% of the HSBGs have IR fluxes measured. About half of them emit, on the average, twice as much energy in the IR than in the blue band; b)
The galaxies with LB > LFIR and a
relatively high surface brightness satisfy a general relation logLFIR
B; (c)
With the increase of the surface brightness the dust
temperature S100/60 asymptotically
approaches 45 K; (d)
The rates of star formation are 10-30 times higher than
those in normal galaxies; (e)
Every year gas with an average mass of 100-300 solar
masses is converted into stars, of which about 10-30 are massive stars. The full text (Petrov,
1989, Ap & Spa. Sci., v. 151, 169-175) could be found here -
in PDF format. 2. AN EVIDENCE FOR ENHANCED STAR FORMATION RATE IN IRAS-DETECTED
ARAKELIAN GALAXIES
The IR emission of 182
Arakelian galaxies (AknGs), included in the IRAS Survey, is considered
as an evidence for enhanced star formation rate (SFR) in them. About
63% of the AknGs have high far infrared luminosities (LFIR
> 1044 erg/s) in 1-500 μm IR spectral band. The
distribution of log (f60/f100
), peaked at about 45 K, shows that IRAS AknGs are considerably warmer
than the "normal" S galaxies. IRAS AknGs have a tendency to extend the
relation f100/f60 vs
LIR/LB for "normal" S galaxies. They emit up to
seven times more IR energy in 40-120 μm band than in
theoptics. The mean ratio <LFIR/LB>
for 148 IRAS AknGs with known redshifts is 3.63. It has been stated that there are two IR emitting components in the IRAS AknGs - a warm one connected with the UV-fluxes of the newborn massive stars, reradiated by dust, and a cool one, originated from the dust in galactic disks and heated by the general interstellar radiation field. The warm IR luminosities and warm IR fractions are determined on the basis of IR colour-colour diagrams α(25/12), α(60/25), and α(100/60). The mean warm IR fraction is 0.55 when the grain mass absorption coefficient model with n = 1.0 is used (or 0.72 if n = 0.0 is adopted). The dust mass
responsible for the IR flux at 60 μm is derived to be about 109
MSun , assuming the dust clouds are optically thin, and
using the dust temperature T ~ 36 K (defined from the f60/f100
ratio). There is a relation between LIR and LB which points out that most of the IRAS AknGs have rather enhanced SFR. On the basis of the
discussion the following conclusions have been made: a) About
63% of IRAS-detected AknGs show high
total IR luminosities LFIR > 1044 erg/s in 1-500 μm IR spectral region; b) The
distribution of log(f60/f100 ) shows that IRAS AknGs are warmer than the "normal" S
galaxies with a clear peak at about T = 45 K (n = 0 model). The
temperature color index f60/f100 of
IRAS AknGs is distributed similarly to that of the blue compact emission-line
galaxies (BCELGs); c) IRAS-selected
AknGs tend to extend the relation f100/f60 vs LIR/LB for "normal" S
galaxies and emit up to seven times more energy in the IR spectral band
between 40 and 120 μm. Its mean ratio <LFIR/LB>
of FIR luminosities to blue ones is about 3.63; d)
It is very likely that in
IRAS-detected AknGs there are two IR components a warm
one, connected with the UV fluxes of newborn
massive stars, reradiated by dust, and a
cool one, originated from dust in galactic disks, which is heated by the general interstellar
radiation field. The ability to deduce the total warm IR luminosities LIR
and warm IR fractions LIR/LB rests on the IR
colour-colour diagrams α(25/12), α(60/25), and α(100/60). The mean warm
IR fraction is < LIR/LB
> ~ 0.55, if the
grain mass absorption coefficient is n = 1.0, or <LIR/LB>
~ 0.72 if n = 0.0; e) If
the dust clouds are optically thin, the dust mass of IRAS-detected
AknGs, which is responsible for IR flux densities observed at 60 μm, is derived
to be Mdust (60 μm) ~ 109
MSun; f) There
is a correlation between
LIR and LB, which indicates that most of the IRAS-detected AknGs have
enhanced rather than constant SFR. 3.
STAR FORMATION IN KARACHENTSEV DOUBLE
GALAXIES The pairs of galaxies
are the simplest systems of galaxies. The study of such systems is of
great interest because of the different
rates of evolution and gravitational and star burst effects. There is a
strong evidence the double galaxies
arised together and their evolution elapsed via parallel ways. IRAS all-sky survey
covered more than 96% of the sky at 12, 25, 60 and 100 mkm. Roughly 11
500 galaxies and quasars have been detected
with positional accuracy 4 x 15 arc. sec
in 1 sigma. The vast majority of the
extragalactic objects detected in the IRAS survey are late type spirals. Elliptical and lenticular
galaxies have rarely been detected. A review of IRAS data of
extragalactic objects has been given by Soifer et al. (1987). We have begun an investigation of star formation in different types of galaxies - HSBGs, Arakelian- and Markarian galaxies using IRAS data. Pairs of galaxies are the only reason to look for some differences in the star formation of the components of the same system. For the beginning we have chosen Karachentsev pairs of galaxies (KarGs). The overall list of Karachentsev contains 603 pairs. a)
The IR KarGs are a sample of normal galaxies with on the
average high IR luminosities - <LgLIR> ~ 43.60; b)
We might expect an increasing or constant SFR than a
decreasing one. This could be explained with the influence of the
neighbour in the pair; c)
To detect IR fluxes from KarGs there have to exist 1E+3
to 1E+8 Mo
dust in these galaxies. For
the arbitrary ratio gas/dust ca. 100 this
leads to 1E+5 - 1E+10 Mo gas; d)
The star formation activity in Karachentsev double
galaxies is lower then in Arakelian-, HSBG or Markarian ones
and is similar to the SFR in bright spiral galaxies in Virgo. 4.
EVIDENCE FOR ENHANCED STAR FORMATION IN IRAS-DETECTED MARKARIAN GALAXIES The IR emission of 640
Markarian galaxies (MrkGs), included in the IRAS Survey, is considered
as an evidence for enhanced star formation rate (SFR) in these objects.
About 73% of the MrkGs have high far infrared luminosities (ca. 10E+44
erg/s) in 1-500 μm IR spectral band. The distribution of log (f60/f100),
peaked at about 45 K, shows that IRAS MrkGs are considerably warmer
than the "normal" S galaxies. IRAS MrkGs have a tendency to extend the
relation f60/f100 vs
LIR/Lbl for "normal" S galaxies. They emit up to
hundred times more IR energy in 40-120 μm band than in the optics. The
mean ratio Lg<LIR/Lbl> for 621 IRAS MrkGs
with known redshifts is 2.2. It is suggested that
there are two IR emitting components in the IRAS MrkGs - a warm one
connected with the UV-fluxes of the newborn massive stars, reradiated
by dust, and a cool one, originated from the dust in galactic disks and
heated by the general interstellar radiation field. The warm IR
luminosities and warm IR fractions are determined on the basis of IR
colour-colour diagrams α(25/12), α(60/25), and α(100/60). The mean warm
IR fraction is <LFIR/LFIR> ~ 0.55 when the
grain mass absorption coefficient model with n = 1.0 is used. The dust
mass responsible for the IR flux at 60 μm is derived to be about 10E+5
Mo, assuming the dust clouds are optically thin, and using
the dust temperature Td ~ 46 K (deduced from the f60/f100 ratio). There is a relation between LIR
and Lb which points out that most of the IRAS MrkG have
rather enhanced SFR. On the basis of the
above discussion the following conclusions have been made: a) About
73% of IRAS-detected MrkGs show high total IR luminosities LFIR
>> 10E+44 erg/s in 1-500 μm IR spectral region; b) The distribution of log(f60/f100 ) shows that the IRAS MrkGs are warmer than the "normal" S galaxies with clear peak at about T = 45 K (n=0 model). The temperature colour index f60/f100 of IRAS MrkGs is distributed similarly to that of the BCELGs; c) IRAS-selected
MrkGs tend to extend the relation f60/f100
vs LIR/Lbl for "normal" S
galaxies and emit up to hundred times more energy in the IR spectral
band between 40 and 120 μm. Its mean ratio <LIR/Lbl>
of IR luminosities to blue ones is about 2.2. d) It
is very likely that in IRAS-detected MrgGs there are two IR components - a warm one, connected with the UV fluxes of
newborn massive stars, reradiated by dust, and a cool one, originated
from dust in galactic disks, which is heated by the general
interstellar radiation field. The ability to deduce the total warm IR
luminosities LFIR and warm IR fractions LFIR/LFIR
rests on IR colour-colour diagrams α(25/12), α(60/25), and α(100/60)).
The mean warm IR fraction is < LFIR/LFIR >
~ 0.55, if the grain mass absorption coefficient is n = 1.0; e)
If the dust clouds are optically thin, the dust mass of
IRAS-detected MrkG, which is responsible for the IR flux densities
observed at 60 μm, is derived to be Md(60 mkm) ~ 10E+5
Mo; f) There
is a correlation between LIR and Lbl, which
indicates that most of the IRAS-detected MrkGs have enhanced rather
than constant star formation rate. The full text (Petrov,
1993, Ap & Spa. Sci., v. 199, 199-213) could be found here -
in PDF format. Click here for more details about star formation in
galaxies from IRAS data. PUBLISHED PAPERS
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