Multi wavelength analysis of Hα-selected
star-forming galaxies @ z~0.8
V. Villar1, J. Gallego1, J. Zamorano1, D.C. Koo2, P.G. Pérez-González3 , A.Gil de Paz4
1 Universidad
Complutense de Madrid (SPAIN), 2 Lick Observatory, University of California (Santa Cruz, USA),
Observatory, University of Arizona (USA), 4 IPAC, California Institute of Technology (USA)
3 Steward
The two narrow band filters
used in this work:
•Our own filter (green curve)
centered at 11810 Å.
• J-continuum filter centered
around 12070 Å (blue curve).
Building the sample
The Hα universe project
Selection technique
The UCM has built several samples of
Hα selected star forming galaxies. The
main goal is to understand the
properties of these objects and to
compare with the universes in UV, FIR
and other SFR tracers…
Several samples were built at different
redshifts to understand the way these
objects evolve.
Emission-line objects are selected from deep
images taken with a narrow band filter
tuned to the redshifted Hα emission line.
Two narrow band filters are being used.
A broad-band image provides the continuum
of reference .
The redshifts targeted are:
• z=0
Local
• z=0.24
Cuasi local
• z=0.4
Transition epoch
J band is used as broad band
(purple curve)
The OH skylines
shown (red curve)
Spectroscopic confirmation
Our collaboration with the DEEP team at Lick
Observatory (University of California, Santa Cruz) allow
us to check the redshift of our candidates. Covered
fields were selected within the DEEP survey areas. The
DEEP team contributes with Keck spectroscopy and HST
imaging.
Our current redshift goal is z=0.8,
where the SFR density is supposed to
reach a maximum and a transition has
been observed in the galaxy population.
http://deep.ucolick.org/
are
also
As part of the DEEP collaboration,
126 HST/ACS orbits have been
already granted to cover the
extended Groth strip. HST images
will provide accurate multi-band
photometry
and
structural
parameters.
GSS 073_4662
A pilot study: Two spectroscopically
confirmed candidates at z=0.8
Here we show images in B, F606, I,
UCM narrow band, IRAC 3.6µm and
IRAC
4.2µm
bands
of
GSS
073_4662. The redshift of this star
forming
galaxy
is
z=0.8095,
provided by the DEEP team.
Deep nIR images (21000s) of the
deep HST/WFPC2 Groth Strip have
been taken with the UCM filter in
order to obtain star forming galaxies
candidates at z=0.8. The candidates
are selected by its color (narrow
band minus broad band) excess.
B
F606W HST
I
NB 11810Å
IRAC 3.6µm
IRAC 4.2µm
GSS 063_6706
Here is the second object confirmed
by DEEP. This one is at redshift
z=0.81520. The same information as
for GSS 073_4662 is shown.
Spectral Energy Distributions
As part of the multi wavelength
analysis we also use GALEX data for
the UV and SPITZER data for the FIR.
Here we show the spectral energy
distributions taking into account B, R,
I, J, K bands and SPITZER 3.6, 4.5,
5.8 , 8.0 and 24.0 µm bands. The
green curve is the M82 spectrum
redshifted to the object redshift. The
fine fit of the SED of the two objects
with M82 spectrum is clear. However,
both objects present an excess in the
24.0 µm.
B
F606W HST
I
NB 11810Å
IRAC 3.6µm
IRAC 4.2µm
GSS 063_6706 SED
Detailed multi wavelength analysis
Keck spectrum for
GSS073_4662.
The most prominent
emission lines of HIIlike galaxies are clearly
seen in the moderate
spectral
(R~5000)
resolution
spectrum
obtained
using
the
LRIS spectrograph at
Keck I.
Half-light
radius
(Re)
vs.
velocity width (σ) diagram for
GSS073_4662 (black diamond).
The typical locations of various
galaxy
types
are
shown,
including E/S0 and spheroidal
galaxies (Bender et al. 1992),
spirals (de Vaucouleurs et al.
1991, RC3), irregulars (RC3)
and local star-forming galaxies
from the UCM sample (red
dots). Dashed lines correspond
to constant masses of 108, 1010
and 1012 M~.
GSS 073_4662 SED
Star formation rate for each
object has been obtained by
different
tracers.
We
compare here the SFRs
obtained through the UV
continuum and IR flux with
the one obtained with the
Hα line flux. Diamonds are
the objects of our sample at
z=0.8. Triangles are objects
around z=0.4 and the
circles are objects around
z=0.8, both selected by
their IR flux.
A FIR-based SFR excess has
been clearly detected for
GSS063.
GSS063_6706
GSS063_6706
GSS073_4662
GSS073_4662
GSS063_6706
GSS073_4662
GSS073_4662
Ratio of SFRIR versus extinction-corrected
SFRHα as a function of LIR.
Diamonds are the objects of our sample.
Filled triangles are galaxies around z=0.4
and filled circles are galaxies around
z=0.8, both selected by their IR flux
(Cardiel et al. 2003). Filled squares are
galaxies in the HDF-S observed by
Rigopolou et al (2000). Asterisks are the
extinction corrected objects from Sullivan
et al (2001). Open circles and stars
corresponds to the local UCM sample.
Our preliminary data tend to confirm
the scenario where larger FIR-based
SFRs are observed in more FIR
luminous star forming objects.