Dwarf Galaxies
Ovidiu Vaduvescu
ING and IAC Associated
ING+NOT+Mercator Seminar
31 May 2012, La Palma
Abstract
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Brief overview about science interests of studying star forming dwarf
galaxies: dwarf irregulars (dIs) and blue compact dwarfs (BCDs);
Strategies for NIR imaging of extremely faint targets. Our smart algorithm to
subtract the highly variable NIR sky;
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Our new sech law to fit SBPs of dIs and BCDs;
Our new “dwarf fundamental plane” (FP) fitting dIs, BCDs and dEs. Some
physical fundamentals of this FP;
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Chemical evolution of dIs and BCDs in clusters and isolated;
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Future projects and search for students/collaborators at ING/NOT/IAC/etc.
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Why dwarf galaxies and NIR?
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Because this was my proposed subject for my Canadian PhD (2000-2005)
at York University in Toronto (Prof. Marshall McCall);
Because dwarf galaxies are the most numerous galaxies in the Universe!
Because they should be the most simple to study, believed to be the first
galaxies to form, from which the larger ones evolved;
Because they are little studied, being very difficult to observe (requiring
large telescopes and long time), due to their extremely faint brightness!
Why observing in Near Infrared (NIR) and not in visible?
- Because NIR light traces better the stellar mass of a galaxy;
- Because NIR is more transparent to dust (internal or Galactic).
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Observing runs: 2-8m telescopes
 OAN-SPM Camila (10n, 2001 & 2003)
 CFHT CFHTIR (6n, 2002 & 2004)
 Gemini North GMOS-N (12h spec, 2003)
 Gemini South GMOS-S (50h Ha img & spec, 2007-2012)
 NTT SOFI (5n, 2006 & 2008)
 Blanco ISPI (10n, 2006-2009)
 VLT HAWK-I (6h, 2008)
 TNG NICS (4n, 2010)
 INT WFC (10n Ha img, 2009 & 2010)
 SAAO IRSF SIRIUS (collab, 2005 & 2006)
 CFHT WIRCAM (collab, 2005 & 2006)
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Observing in the NIR:
The problem with the rapidly variable sky (in level and structure)
More difficult than in visible!
It is very important HOW we
observe in the NIR (how often
sample the sky to be subtracted
every ~minute).
Movie showing Mauna Kea sky
and CFHT environment variations
in Ks band during 2 min step
(timelapse 20 min). Variations
across the 3.6' CFHT-IR chip
about 1% of the sky level are
visible.
(Vaduvescu & McCall, 2004)
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Observing faint galaxies in the NIR
Giving the sequence:
sky-gal-sky-gal-sky-....
If one combines the sky
observed less frequently,
the final combined
galaxy gets worse.
Thus, a so-called
“superflat” in the NIR
destroys the temporal
sky variation!
We invented a smart
algorithm to “build” and
subtract the sky “under”
the galaxies in the NIR.
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Our algorithm to reduce NIR images
How to build and subtract the sky “under” the galaxy
assuming the observing sequence sky1-gal1-sky2-gal2-....
Step 1: raw sky
Step 2: Subtract sky1-sky2
(to see all stars)
Step 3: find all stars (daofind)
Steps 4-6: mask stars
(imedit or daophot/PSF)
Step 7: add back raw sky2
(to fill back all black holes)
Step 8: do these again for
sky2-sky1 and average the final
reduced sky to interpolate time
Remember first raw sky/step1?
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Our algorithm to reduce NIR images
How an extremely faint galaxy shows up following accurate sky subtraction
Step 1 gal: raw galaxy
(can you find it? :)
Step 2 gal: galaxy sky
subtracted (sky built like before)
Step 3 gal: combined galaxy
(some black hole residuals due
to bright stars, background
galaxies in the sky field or
insufficient large dithering)
Step 4 gal: mask residuals
(manual imedit or other) –
final reduced galaxy image
Remember first raw galaxy
(step1)?
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KILLALL, an IRAF software
to remove stars from an image
NGC 1569 (our most
complicated studied dwarf):
There are about 5000 stars
in the first image, including
some 2500 on top of the
galaxy!
They can be removed semiautomatically in 5 steps using
KILLALL (DAOPHOT/PSF
based script) one day work
Buta & McCall, 1999 (UNIX)
Vaduvescu & McCall, 2001
(ported in Linux)
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Dwarf Irregular Galaxies (dIs)
They have surface brightness
profiles (SBPs) linear in the
outer part and bounding
horizontal at the centre.
We invented a new “sech”
law to fit SBPs of dIs
(Vaduvescu et al, 2005):
Why is this? Not known.
Could be investigated
(modeling – collaborators?)
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The dIs Fundamental Plane (FP)
The linear Tully-Fisher relation
does not appear to hold for dIs.
Instead, three physical
parameters link dIs in a
Fundamental Plane (FP)
(Vaduvescu et al., 2005,
Vaduvescu & McCall, 2008):
- Sech absolute mag MS
- Central surface brightness o
- Hydrogen line width W20 (radio)
This FP can be used as a new
distance indicator (for dwarfs or
others): if we measure o and
W20, then we can calculate M,
thus the galaxy distance modulus
and distance!
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Fundamentals of the dwarf FP
The baryonic potential plane assuming fixed M/L (left)
and individualized virial conditions (right).
Standard deviations are 0.29 mag, similar to that of TF relation for giants!
(McCall, Vaduvescu et al., 2012)
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NIR CMDs of dIs
Near Infrared (NIR) Color-Magnitude Diagrams (CMDs) for the stars resolved in
two dwarf irregular (dIs) galaxies. Two main details can be seen: the main bulk
and a “finger” (Vaduvescu et al 2005). Is the tilt metallicity-dependent?
Is the “whole” real? Again, collaborators welcomed!
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Blue Compact Dwarf Galaxies (BCDs)
BCDs have surface brightness
profiles linear at the outer parts
and growing then bounding
horizontal at the centre.
Fitted with the “sech” law to
count the outer regions (dashed
line) plus a Gaussian to model
the central BCD starburst
(dotted line) - Vaduvescu,
Richer & McCall, 2006:
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BCDs and the dIs FP
Blue Compact Dwarfs (BCDs)
seem to be located on the FP
defined by dIs.
This probes a physical link
between the two dwarf classes.
The FP stands as a distance
indicator for BCDs, also.
(Vaduvescu, Richer & McCall,
2006)
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Dwarf Ellipticals (dEs) and the dIs FP
Dwarf Elliptical galaxies (dEs) stand on the dIs FP, suggesting a physical link
between the three dwarf classes (dIs, BCDs and dEs) (Vaduvescu & McCall 2005).
In comparison (left), Tully Fisher relation shows larger scatter (Vaduvescu et al,
2005). New dE NIR data available to probe this (collaborators welcomed)!
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Chemical evolution of dIs and BCDs
Chemical properties in star
forming dwarf galaxies
can be measured via
spectroscopy, namely the
oxygen abundance.
Best results are achieved
via [OIII] 4363 line
(“direct method”), but this
is very faint to observe,
requiring ~8-10m class
telescopes (=> GTC !)
Alternatively, use other
bright line methods (less
accurate)
(Vaduvescu, McCall &
Richer, 2007)
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Chemical evolution of dIs and BCDs
Oxygen abundance correlates
with absolute sech magnitude
in both dIs and BCDs, and in
the NIR the relation is tighter
than in visible
12+log(O/H)=5.58-0.14log(MS)
(rms=0.10)!
(Vaduvescu, Richer & McCall
2007)
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Chemical evolution of dIs and BCDs
In a closed box model,
metallicity is expected to
correlate with the gas fraction,
μ = Mgas/(Mgas+Mstars)
BCDs and dIs appear to obey
this model (although we need
to improve the sample),
suggesting a chemical relation.
(Vaduvescu, Richer & McCall
2007)
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Dwarf evolution in clusters
To compare star forming galaxy isolated evolution (Local Volume d<10 Mpc)
with the evolution of dwarf galaxies in nearby galaxy clusters (d<100 Mpc) and
higher redshift.
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Virgo (14 Mpc)
Fornax (17 Mpc)
Hydra (49 Mpc)
Antlia (35 Mpc)
Perseus (5 Mpc)
Abell 779 (92 Mpc)
Abell 1367 (90 Mpc)
Others with WHT, GTC, etc.
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Dwarf evolution in clusters
Compared with the LV
(isolated objects), star
forming dwarfs in Virgo
appear to obey the same FP,
while Hydra appear to suffer
some enviromental effects.
Fornax sample is insignificant
for any conclusions, and
needs increased.
(Vaduvescu, Vilchez, Kehrig,
et al, 2011).
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Dwarf evolution in clusters
Apparently, the chemical
evolution looks similar in
Virgo, Fornax and Hydra,
as seen through the
closed box model.
New GMOS spectroscopic
data was acquired
recently in Antlia cluster.
(Vaduvescu, Kehrig,
Smith-Castelli, Richtler
2011 & 2012) – in
reduction.
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Collaborators
 Prof. Marshall McCall, York Univ, Canada;
 Dr. Robin Fingerhut, York Univ, Canada;
 Dr. Michael Richer, OAN-SPM, Mexico;
 Students Francisco Pozo and Angie Barr, UCN Chile -> Bochum Univ;
 Prof. Dr. Eduardo Unda-Sanzana, UCN -> UA, Antofagasta, Chile;
 Dr. Marcus Albrecht, UCN -> Univ. Bonn, Germany;
 Dr. Analia Smith-Castelli, La Plata, Argentina;
 Dr. Lidia Makarova, SAO, Russia;
 Prof. Dr. Jose Vilchez, IAA, Granada, Spain;
 Dr. Carolina Kehrig, IAA, Granada, Spain;
 Dr. Jorje Iglesias-Paramo, IAA, Granada, Spain;
 Drd. Vasiliky Petropoulou, IAA, Granada, Spain;
 Dr. Daniel Reverte, GTC La Palma.
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Future work
 Improve the dwarf FP using new radio data (Paolo Serra + new HI surveys)
and deeper NIR data to study further the phsyical link between dIs and BCDs;
 Enlarge the dE NIR sample (Blanco 2009 run, Peletier collab, first release of
VISTA, etc) and study their relation with star forming dwarfs;
 Approach the relation of our dwarf FP with other classic FPs for giants, in the
attempt to constraint their physical evolution.
 Due to my present busy support job and other science interests (and also
because I became a father!) I need students or collaborators to continue these
line of research. Eventually I could co-supervise one PhD student together with
another thesis director (from IAC, ULL or others from abroad).
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References
http://www.ovidiuv.ca/papers/
Vaduvescu, O. and McCall, M., 2004, PASP 116, 640
Strategies for Imaging Faint Extended Sources in the Near-Infrared
Vaduvescu, O. et al, 2005, AJ 130, 1593
Infrared Properties of Star-Forming Dwarf Galaxies. I. Dwarf Irregular Galaxies in the Local
Volume
Vaduvescu, O., Richer, M., and McCall, M., 2006, AJ 131, 1318
Infrared Properties of Star-Forming Dwarf Galaxies. II. Blue Compact Dwarf Galaxies in the
Virgo Cluster
Vaduvescu, O. and McCall, M., 2005, Proc. IAU No. 198
dEs and the dI fundamental plane
Vaduvescu, O., McCall, M. and Richer, M., 2007, AJ 134, 604
Chemical Properties of Star-Forming Dwarf Galaxies
Vaduvescu, O. and McCall, M., 2008, A&A 487, 147
The fundamental plane of dwarf irregular galaxies
Vaduvescu, O., et al. 2011, A&A 553, 95
Searching for Star Forming Galaxies in Fornax and Hydra Clusters
McCall, M., Vaduvescu, O., et al. 2012, A&A 540, 49
Fundamentals of the Dwarf Fundamental Plane
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