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 Arakelian’s 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

 

  1. PETROV G. T. , Ap & Spa. Sci., v. 151, 169-175, 1989                                                        
    “Star burst activity in High Surface Brightness Galaxies“
  2. PETROV G., YANKULOVA I., C. r.Acad. Sci. Bulg., v. 43, No. 11,1990                                                                     “Surface brightness and Starformation in Arakelian galaxies“
  3. PETROV G., C. r. Acad. Sci. Bulg., v. 44, No. 4, 1991                                                                                          “Markarian galaxies in the far-infrared - an analysis of IRAS data“
  4. PETROV G., YANKULOVA I., C. r. Acad. Sci. Bulg., v. 44, No. 4, 1991                                                                  “Evidences for high star formation activity in the Arakelian galaxies“
  5. PETROV G., C. r. Acad. Sci. Bulg., v. 44, No. 5, 1991                                     
    “Statistical comparison of the basic parameters of high surface brightness and normal galaxies“
  6. PETROV G.,  Ap & Spa. Sci, v. 199, 199 - 213, 1993  
    “An evidence for enchanced star formation in IRAS-detected MrkG“
  7. JANKULOVA I., GOLEV V., PETROV G., Astrofiz. Issled. (Izv. SAO), v. 35, 60-75, 1993 
    “An evidence for enchanced star formation rate in IRAS-Detected Arakelian galaxies“

 



Created by G. T. Petrov