Blue Compact Galaxies as building blocks: Kinematics & Lyman-alpha studies

taupeselectionMechanics

Nov 14, 2013 (3 years and 8 months ago)

84 views

Blue Compact Galaxies

as building blocks:

K
i
nematics

& Lyman
-
alpha studies


Göran

Östlin

Department of Astronomy

Stockholm University

BCG kinematics


See talks by
Marquart

and Cumming

Objectives:


Trace the dynamics of these objects


Study dynamical mass estimates in comparison
with stellar mass distribution


Feedback processes


Evolutionary status and fate: rotationally
supported/dispersion


will become
dIrr

of
dE


CIGALE F
a
bry
-
Perot observations of ~ 50
BCGs

in Hα

UM sample (M
a
rquart
,
Östlin

et al in prep)
-

Tvice

as many in hand

2/3 of objects show apparent non equilibrium dynamics

Is Hα a good tracer? (Feedback)

Case for
CaT

observations


Hα kinematics suggest that MERGERS are important,
but




Feedback processes may affect the ionised gas i.e. Hα


Can we get information on the motion of stars? From
CaT

yes!


Not a replacement (because its damn hard) of Hα but a
reality check


How wrong can we do if we just use Hα
at low and high
z
?


Result (so far): Stellar velocities sometimes different
from Hα but never regular when Hα is not


Are we really tracing the potential?

Luminous
BCGs

at higher
z

LBCGs

are Locally rare but
common at high
-
z
:


S
pace density increase by
10 to
z
=1

Responsible for up to 50%
of
incresae

in UV SFR


Puech

et al (2006) studied
17
LBCGs

a
t

intermediate
z

in [OII] using
VLT/FLAMES/IFU

Stellar
vs

dynamical masses at
z
=0 and 0.5

Östlin

et al 2001 / CIGALE

Guzman et al. 2003 / LRIS

Are we seeing the same objec
t
s or not?

Puech
, Hammer, Flores,
Östlin
,
Marquart

2006

Most intermediate
LBCGs

are not rotationally supported

Complex and perturbed kinematics common


Mergers?

Dynamical masses only indicative

IMAGES and perspectives


A surprisingly low fraction of rotating stellar disks
at
z
=0.6 (
N
eichel

et al 2008), factor of two
incresae

to
z
=0


Strong evolution of galaxy kinematics since
z
=1
(Yang et al 2008). More than 40% of
all
intermediate mass (log(M)~10) galaxies are
perturbed


The mergers and starbursts are there, but do
what (
cf

Noeske
)?


Bursts must be short (OK) or we have dry mergers
(no)

A comment on BCG starburst triggers


Our kinematic studies suggest mergers are important for
starburst triggering, at least at high L (and give lots of
SSCs
, see
Angela’s talk)


At low mass stochastic starbursts are conceivable (
Gerola

fashion)


no trigger


But what about interactions (see
Sungs

talk)


my feeling is
that tidal forces are to weak in well separated dwarf galaxy
pairs:


T
idal

force
criterium
:
d

< (M
comp
/M)
1/3
R


R=10
kpc
,
M
comp
=10
12
,M=10
9



d
<100
kpc

(Campos et al 1993)


Cf

large galaxies (
Bergvall

et al 2004, AA 405, 31), dwarf should
be even worse


If mergers are
resposible

we will not necessarily see
companions. Are these misleading us?


The BCG
-

GRB connection

Sollerman
,
Östlin
,
Fynbo

et al. 2005
NewA

11,103

Christensen et al. 2004:

GRB hosts have higher SSFR than

95% of the HDF galaxies

But
BCGs

match pretty well!

(K
nown

GRB+SN hosts by 2005)

Lyman alpha in local starbursts


and beyond

TEAM


Göran

Östlin


Matthew Hayes (Geneva)


Daniel
Kunth
, H
a
kim

Atek

(IAP)


Miguel
Mas
-
Hesse

(Madrid)


Claus
Leitherer

(
STScI
)


Artashes

Petrosian

(
Byurakan
)

Why study
Lyα

?


Strongest recombination line: Lyα/Hα≈10,
E
W
max, rest

= 240 Å


One third of all ionising photons reprocessed
to
Lyα


Visible at high
-
z
, contrary to Hα


Narrowband studies
now
efficient in yielding
large numbers of high
-
z

Lyα

emitters


Can probe
reionisation

Leitherer

/ Starburst99

Background


Early studies at high and low
z

(IUE) showed
Lyα

to be unexpectedly weak


R
esonant

scattering and dust?


But the most metal
-
poor and dust
-
poor local

S
tar forming dwarfs are damped
Lyα

absorbers

(e.g. IZw18, SBS0335
-
052, Tol65)

Local star forming galaxies (IUE):

Lyα

is weak and cannot be
extinctioncorrected

High
z

Lyα

imaging and

spectroscopy

LBGs

and
LAEs

are
not
the
same population: only 25% of
LBGs

show
Lyα


E
W
s

can reach well above
240Å (Rhoads &
Malhotra

2004):

popIII

or
radiative

transfer
effects

A (dusty) multiphase medium can in fact also
enhance
Lyα

(Neufeld 1991)

Can boost EW

Edge on starburst

HII region dynamical
evolution


A
ccelerate

HI

Promotes
Lyα

escape


Tenorio
-
Tagle

Lyman alpha


When seen in emission, frequently with P
-
cyg

profile


ISM absorption lines reveal neutral gas
outflow


But the
Lyα

should come out somewhere in
cases where dust content is small




Imaging of local objects needed

Haro11

Hayes et al. 2007

Lyman alpha surface photometry

20x20
arcsec
, 3.5
x

3.5
kpc

ESO 338
-
04

(a.k.a. Tol1924
-
416)

ESO 338
-
04

SSCs

and Ly
-
alpha

0.2






0.1






0

ESO338
-
04



Observed



Corrected

for


internal

extinction

Model

Observed

local/HST

Equivalent

width

of
Lyα

and


should

be
positively

correlated

but

are not !

-

For
LBGs

at z=3, median EW(Lyα)=0 Å

-

Semianalytic

models

can

match data
if

f
esc
=2%


-

Dust
only

part of the story



Local

observations SA
model

Summary

of
results
:



First
calibrated

Lyα

maps

produced


spatial resolution ~10
-

20 pc


soon

to be
released

to public


Substantial

evidence

for
Lyα

resonant

scattering

presented
:


morphologies
,
scattering

halos,
extended

emission


Local

super
-
recombination

values


Lyα

emission from
old

and/or
dusty

regions


Low

escape

fractions

(< 20%)
--

dust
corrections

fail

(
<50
%)


When



strongest

(
starburst

youngest
)
Lyα

weakest


Demonstrates

the
need

for a
detailed
,
statistically

sample