Transcript [Segundo ejercicio]

SED OF NORMAL GALAXIES
Josefa Masegosa *, Isabel Márquez*, Brigitte Rocca-Volmerange * *, Michel Fioc * * & Damien Leborgne***
*Instituto de Astrofísica de Andalucía (C.S.I.C.), Granada (SPAIN)
**Institut d’Astrophysique de Paris (IAP), Paris (FRANCE)
***CEA, Saclay (FRANCE)
Sa
INTRODUCTION
With the aim to get a first insight on the reliability of PEGASE.3 to investigate SED evolution of galaxies, we have studied a large
sample of spiral galaxies avoiding systems with Starburst or Nuclear Activity.
Sb
We have selected a large sample of normal galaxies according to the following IR criteria :
s60/100 < 0.45
Sc
Sd
s12/25 > 0.60
(Helou et al 1987, Masegosa & Márquez 2005)
With this definition we granted the exclusion of Starburst and/or AGN systems.
All the galaxies in the IRAS Faint Source Catalog (FSC) with accurate fluxes in the 4 IRAS bands (quality flag 1) were selected. This
results in a sample of 15 Sa, 26 Sb, 77 Sc and 9 Sd galaxies. Their spectral energy distribution (SED) from far-UV till far-IR is
studied by using the data provided by NED.
Fig. 1. s12/s25 and s60/s100 ratios are presented for the four
morphological types Sa, Sb, Sc and Sd. The filled histograms
correspond to the galaxies with a reliable SED fitting.
Fig. 2. SED fitting (full line) to the observed UVoptical to far IR magnitudes (dots connected by
straight lines). Examples for the four
morphological types are presented. In the bottom
right box of each pannel the main output
parameters are shown.
PEGASE.3
PEGASE.3 is an improved version of the spectral
evolution code by Fioc & Rocca-Volmerange (1997). It
takes into account the effect of dust, which absorbs and
scatters optical and UV photons that re-emit in the IR
and submm range. For a given evolutionary scenario (star
formation law, initial mass function, infall rate, etc.),
PEGASE consistently computes the following quantities:
- Metallicity of the ISM and of newly formed stars
- Amount and composition of the dust
- Attenuation of the stellar radiation by dust using a
radiative transfer code
- Grain re-emission in the IR, taking into account the
stochastic fluctuations of temperature
- SED and colors of a galaxy from the far-UV to the far
IR-submm range.
SED ANALYSIS
Fig. 3. Average SED for the four morphological types, normalized
to K magnitude.
AVERAGE PROPERTIES OF NORMAL SPIRAL
GALAXIES
Our color selection produces a sample of normal galaxies
dominated by Sc and Sb galaxies, and with Sa and Sd spirals
less well represented. A range in luminosity between 109 and
1011 Lo is found. There is a trend for spiral galaxies of later
types to be brighter in the Far Infrared (see Fig. 4).
The scatter is reduced when considering luminosity ratios,
both for LFIR/LB and LFIR/LK (Fig. 5), excepting for the Sa,
that cover the largest range in LFIR/LB. The galaxies with
reliable SED fitting (full histograms) constitute a more
homogeneus family for each type, with smaller scatter.
Specific star formation rates (SF per unit mass), provided by
LFIR/LK , are the smallest for Sa, increasing to Sb and Sc. A
similar conclusion is reached by Dale et al. (2006), whereas
their trend is less clear mainly due to the inclusion in their
sample of star forming and/or active galaxies.
We collected data on optical UBV, near IR JHK integrated
magnitudes for all the galaxies and performed the SED fitting
for each individual galaxy. By using a template of the same
morphological type than each target galaxy, we found that a good
fit, parametrized by both χ2 and visual inspection, can be
obtained for 60% of the Sb and Sc galaxies and 30% of the Sa.
For the remaining galaxies no good fits were found due to
different reasons:
● Sa appear to be a rather heterogeneous family with only 30%
of them with a well defined optical morphology. For the
remaining 70%, large departures from Sa morphology are found:
external rings, interacting galaxies (entering into the IRAS
beam), distorted morphologies, etc. Then the use of an Sa
template for them is a simplistic aproximation.
● Sb and Sc are better defined, with smaller dispersion in the
empirical SED which translate into a large percentage of well
fitted galaxies (60%). For the 40%, not well fitted cases, we have
found good fits in the medium to far IR range at the price of
getting large departures at UV-optical frequencies. A closer
inspection of these galaxies has shown that most of them seem to
be barred galaxies, and thus an extra component needs to be
included.
● Sd show a rather good fitting by using Sd template only for 3
galaxies. For the others 6 an Sc template better reproduces the
observed SED, reflecting a poor classification among the Sd
family.
Fig. 4.
Far IR luminosities
(8-1000 μm) for the
four morphological
subclases coded as in
Fig. 1.
Examples of good spectral fittings for each morphological type
are shown in Figure 2.
An average SED for each morphological type is shown in Figure
3. Galaxies with poor fitting have been excluded get these
averaged SEDs.
CONCLUSIONS AND WORK IN PROGRESS
 PEGASE.3 provides a rather good representation for the SED of normal galaxies, selected by FIR colors.
 It produces reliable fits for well defined Sa and for a large percentage of Sb and Sc.
This percentage is higher when only unbarred galaxies are considered. Rather poor fittings are obtained
for Sd due to missclassification problems based on NED morphologies.
 Specific star formation efficiencies increase for later types, i.e., the star formation per unit mass is higher for Sc than Sb, and for Sb than
for Sa.
In this work, fixed fitting parameters as galactic extinction and inclination have been used for this first evaluation of the reliability of
PEGASE.3. SED fitting will be improved by fine tunning of the input parameters.
The subsequent work will consist on the analysis of the SED for Starburst and/or AGN systems including these components in PEGASE.3
models.
Fig. 5. The actual SF efficiency and SSFR can be estimated through
LFIR/LB and LFIR/LK ratios. In the figure we show both for the four
morphological types coded as in Fig. 1.