Download Star Formation in Different Galaxy Types

Magellanic Cloud Star Formation
Bridging the Gap between Milky Way and Distant Galaxies
Star Formation
in Different Galaxy Types
Eva K. Grebel
Astronomisches Rechen-Institut
Zentrum für Astronomie
der
Universität
Heidelberg
Grebel: Star Formation
in Different
Galaxy Types
0
22.02.2013
Integrating over stellar mass
range of 108 < M"/M! < 1013.
Growth
of Global
Stellar Mass
Density
50%
25%
! ~ 45% of the
present-day
stellar mass was
produced in ~
3.6 Gyr from
1 < z < 3.
Marchesini et al. 2009,
ApJ, 701, 1765
22.02.2013
5%
Global stellar
mass density
! Remaining 50%
formed in the
last 7.5 Gyr
from 1 < z < 0.
10%
Redshift
Grebel: Star Formation in Different Galaxy Types
1
Metallicity Evolution
Mass-fraction-weighted
metallicity of > 300,000
SDSS galaxies:
! Mass-metallicity relation
(metallicity ! w. mass)
! Average metallicity of
L" galaxy: solar.
! Below L": decreases by
~ 0.5 dex per dex in mass.
! M" > 1011 M!: flattening.
Panter et
al. 2008,
MNRAS,
391, 1117
! Small metallicity spread
at high masses (0.15 dex);
higher at low masses ( ~
0.5 dex).
Caveat: SDSS fibre size # metallicity bias
22.02.2013
Metallicity
Evolution
Grebel: Star Formation in Different Galaxy Types
2
Ages younger
than 0.5 Gyr
Considering only
age bins < 0.5 Gyr:
Panter et
al. 2008,
MNRAS,
391, 1117
! No more massmetallicity
relation (flat);
not yet clear
why.
! Only galaxies
with stellar masses M" < 1010 M! contribute significantly to
metallicity of young populations (! downsizing).
! Mass range spanned now only 1.5 dex; very few galaxies contribute.
Downsizing: Stars in more massive galaxies tend to have formed earlier
and over a shorter time period.
22.02.2013
Grebel: Star Formation in Different Galaxy Types
3
M87, Virgo
NGC 1316, Fornax
E1
E pec, cD, S0, Sa pec...
Ellipticals:
! Bulk of the star formation at early times.
! Considerable and rapid enrichment.
! Little to no cold gas. Highly ionized gas.
! Generally considered quiescent at present time.
22.02.2013
Grebel: Star Formation in Different Galaxy Types
4
The Extremes: High-z QSOs (z > 6; tUniverse ! 900 Myr)
Bulk of star formation in ellipticals: how early?
$ Metal lines in z > 6 QSOs; sometimes super-solar.
22.02.2013
1500
Mg II
Ly "
1000
2000
2500
3000
Rest frame wavelength [Å]
Grebel: Star Formation in Different Galaxy Types
Fe II
$ Extremely rapid early en! richment within only a few
! 100 Myr (in contrast to spirals).
O I / Si II N V
S i IV / O IV
C IV
$
$
F# [10–17 erg s–1 cm–2 Å–1])]
!
!
!
!
!
! Dust detected $ SNe II-origin, not AGB (time scales).
! Other QSOs dust-free $ onset of massive SF varies.
Mg (Mg II): "-element produced in SNe II.
SNe II form “as soon” as massive stars form.
Fe (Fe II): SNe Ia (minimum
Composite spectrum
delay time 300 Myr)
of QSOs at z > 6
(Kurk et al. 2007,
Fe II/Mg II ratio: ~ constant
ApJ, 669, 32)
as f(z) since z ~ 6
Formation of SN Ia
progenitors at z > 10.
5
The Extremes: High-z Galaxies
Galaxy A1689-zD1: z ~ 7.6.
$ Only detectable in the infrared.
" 13 billion lightyears away from us.
$ Only 700 Myr after Big Bang!
"
"
"
Strong star formation activity (! 7.6 M!/yr).
Star ages of about 45 – 320 Myr.
Star-forming knots with < 300 pc diameter.
"
"
"
Mass in stars: 1.6 – 3.9 " 109 M!.ƞ
(Milky Way: 20 – 40 x more.)
Size: at least 2 kpc. (Milky Way: > 30 kpc.)
Bradley et al. 2008, ApJ, 678, 647
22.02.2013
Grebel: Star Formation in Different Galaxy Types
6
The Extremes: High-z Galaxies (z = 7 to 8)
! SEDs from NIR imaging data of galaxies at z of 7 and 8
! (lookback times of 770 – 640 Myr) show median stellar
! population ages of ~ 200 Myr.
! Typical stellar masses of galaxies at z ~ 7: 109 M!;
! at z ~ 8 possibly as low as 107 M!.
! Some 106 M! of dust from SNe II (from 12 – 35 M! stars).
! Time scales: ~ 20 Myr.
! Increase in dust extinction from very low amounts at z ~ 7
! to AV ~ 0.5 at z = 4. Time scale for this increase consistent
! with low-mass AGB stars forming bulk of the dust.
! Most galaxies at z ~ 7 with metallicities of 0.005 Z!;
! some with 0.02 Z!.
! Colors resemble local, metal-poor star-bursting dwarf galaxies
Finkelstein et al. 2010, ApJ, 719, 1250; 2012, ApJ, 756, 164
22.02.2013
Grebel: Star Formation in Different Galaxy Types
7
Specific
Star Formation Rate
as Function
of tlookback
for EarlyType Gal.
Thomas et al. 2010,
MNRAS, 404, 1775
Intermediateand low-mass
galaxies get
rejuvenated via minor star formation events below redhift z ~ 0.2.
Fraction of young, rejuvenated galaxies increases both with decreasing
galaxy mass and decreasing environmental density to up to 45%.
$ Impact of environment increases with decreasing galaxy mass.
Specific star formation rate sSFR = SFR / M#
22.02.2013
Grebel: Star Formation in Different Galaxy Types
8
Elliptical Galaxies: SFH
Analysis of > 14,000 early-type galaxies in SDSS (volume-limited):
% Age, metallicity, "-enhancement increase with galaxy mass (!).
% Field early-types younger by ~ 2 Gyr than cluster counterparts.
counterparts.
% Negative radial metallicity gradients $ masses and environments.
environments.
% Positive radial age gradients for early-types with ! > 180 km/s.
& Low-mass halos with gas & stars accreted mainly at z ≤ 3.5.
& Earlier accretion in dense environments than in field.
& Fossil populations mainly at large radii
(dissipationless stellar accretion)
Clemens et al. 2009, MNRAS, 392, L35
% ~ 30% of the massive early-types shows some recent (< 1 Gyr)
Gyr) SF!
% Ellipticals:
Ellipticals: ~ 29%, lenticulars:
lenticulars: ~ 39%
% Fraction of UV-bright early-types 25% higher in low-density
environments.
environments.
Schawinski et al. 2007, ApJS, 173, 512
22.02.2013
Grebel: Star Formation in Different Galaxy Types
9
E+A Galaxies
% Spectra of ellipticals (Mg, Fe, Ca absorption; K")
+ strong Balmer lines (A") ' SF within last Gyr
but no [OII] ' no recent SF.
SF.
& Post-starburst galaxies (radio: not dusty starbursts
obscuring [OII])
% In clusters and in field.
% About 30% show disturbed morphologies
% or tidal tails.
Goto et al. 2005, MNRAS, 357, 937
% Young E+A galaxies have more companion galaxies
within 100 kpc.
% E+A galaxies have 54% higher probability of having
companions than normal galaxies (~ 5%).
& Likely merger/interaction origin.
22.02.2013
Yamauchi et al. 2008, MNRAS, 390, 383
Grebel: Star Formation in Different Galaxy Types
10
Global (present) Star Formation Rates
gas content
~ 0 M!/yr
~ 20 M!/yr
starburst galaxies:
up to ~ 100 M!/yr
ULIRGs: up to 1000 M!/yr
22.02.2013
Grebel: Star Formation in Different Galaxy Types
11
Specific Star Formation Rate vs. Galaxy Mass
Mass dependence of the sSFR
via dust-corrected FUV
measurements of SDSS galaxies:
Clear separation between red
and blue sequences.
Dispersion of sSFRs within
blue sequence very small
$ Self-regulation mechanism.
Sharp increase of inactive
galaxies above a few 1010 M!.
Blue sequence: sSFR ! with $
galaxy mass such that lower-mass
galaxies are forming relatively higher
fraction of their stellar mass today.
Schiminovich et al. (2007)
Kennicutt & Evans (2012)
Dominant SF galaxy population “migrated” from
massive to less massive galaxies over cosmic time.
22.02.2013
Grebel: Star Formation in Different Galaxy Types
12
[Fe/H]
Spirals: The Milky Way
Age-metallicity evolution of the
different Milky Way components
Buser 2000, Science, 287, 69
Freeman & Bland-Hawthorn 2002, ARA&A, 40, 487
Kennicutt & Evans 2012, ARA&A, 50, 531
22.02.2013
Radial distribution of surface
densities of atomic gas, molecular
gas and SFR for the Milky Way.
Grebel: Star Formation in Different Galaxy Types
13
Disk Galaxy Evolution
Stellar halos of disk galaxies:
Milky Way stellar
halo today
(simulation,
Cooper et al.)
! Probably formed from inside out.
!
!
!
!
!
!
In galaxies with few recent mergers ~ 20 to 50%
of the stars formed in situ (according to %CDM simulations).
(Zolotov et al. 2009).
Halos dominated by early accretion: higher ["/Fe] expected.
If mainly accretion of high-luminosity satellites: higher [Fe/H].
(Johnston et al. 2008)
! MW inner halo: Accretion of a few moderately metal-rich, 108 –
! 1010 M! Magellanic-sized
Halo substructure traced by
SDSS main-sequence
main-sequence stars.
! satellites > 9 Gyr ago.
! (De Lucia & Helmi 2008)
! MW outer halo: Mainly low! mass, low-metallicity
Bell
! satellites.
et al. 2008
22.02.2013
Grebel: Star Formation in Different Galaxy Types
14
Disk Galaxy Evolution
Bulges of disk galaxies:
!
!
!
!
!
!
!
!
$
!
!
!
!
!
!
Classical bulges: S0 – Sbc. Pseudobulges: later than ~ Sbc.
All bulges show some amount of ongoing SF, regardless of type
(Fisher et al. 2009).
Small bulges formed 10 – 30% of their mass in past 1 – 2 Gyr
(Thomas & Davies 2006).
Massive clumps forming at early times in galactic disks move
towards galactic center due to dynamical friction, merge, and
form bulge (Noguchi 1999).
Trend of ! bulge-to-disk ratios with ! galactic masses.
Most galaxies at z ~ 1: disk-like morphologies, but most galaxies
at z > 2 look clumpy/chaotic (van den Bergh 2002).
Clump masses: 107 – 108 M!. Clump coalescence resembles
major merger in terms of orbital mixing, but no increased DM
content. (Elmegreen et al. 2008, 2009).
Other bulge formation scenarios: Mergers, secular evolution.
22.02.2013
Grebel: Star Formation in Different Galaxy Types
15
6 Gyr ago
Disk Galaxy Evolution
Disks of disk galaxies:
!
!
!
!
!
!
!
Even at z < 0.6 – 0.8: 46%
of the spirals are still chaotic.
Only ~ 5% of Sa/Sab galaxies
are peculiar at z ~ 0.7, but
almost 75% of Sbc and Sc
types are still peculiar.
!
!
!
!
SF activity in clumpy disks
may be caused by local gravitational collapse w/o external
trigger (Elmegreen et al. 2007).
(van den Bergh 2002)
Delgado-Serrano et al. 2010
! Environment: Fraction of
! spirals declines with density
! (e.g., Poggianti et al. 2008).
22.02.2013
Grebel: Star Formation in Different Galaxy Types
16
Sites of Star Formation
Typical present-day sites of star formation in galaxies:
% Extended disks of spirals and irregulars
% Dense gas disks in galaxy centers (circumnuclear SF)
% Enhanced SF in interacting galaxies and starbursts
& Significant contributors to SF in the (local) Universe
Occasionally:
% Intragalactic SF in tidal tails
22.02.2013
Grebel: Star Formation in Different Galaxy Types
17
Spirals and Irregulars: Star Formation “Demographics”
Area-averaged SFR
vs. absolute SFR:
ii
rad
F
S
nt
a
t
ns
co
f
o
es
Lin
SFRs have range of
more than 7 orders
of magnitude.
Largely due to nonequilibrium systems
(starbursts).
Normal galaxies:
Tight range of
SFRs per unit area.
Quiescent SF galaxies
form < 20 M! / year.
Kennicutt & Evans 2012
Starburst galaxies,
Absolute SFR
LIRGS and ULIRGS: Most of the galaxies
in the upper 2 – 3 decades of absolute SFRs and area-averaged SFRs.
22.02.2013
Grebel: Star Formation in Different Galaxy Types
18
Spirals and Irregulars: Star Formation “Demographics”
Three different star formation regimes:
11HUGS
lower
specific
SFRs
SFR & M(H2)
MB ~ –19
~cont.
SFRs
SFR & M(HI)
bulgedomin.
galaxies
Vmax ~ 120 km/s
Vmax ~ 50 km/s
MB ~ –15
irregulars
large
scatter
in spec.
SFRs
spiral
structure
key
regulatory
factor
internal processes dominate
(esp. feedback)
Lee et al. 2007, ApJ, 671, L113
22.02.2013
Grebel: Star Formation in Different Galaxy Types
19
Bothwell et al. 2009, MNRAS, 400, 154
Stellar Mass versus Specific Star Formation Rate
22.02.2013
High-mass
regime:
Late
types
Secularly evolving
intermediate-mass
populations
Low-mass regime:
larger scatter;
Some galaxies with
anomalously low SFR.
Some tendency
for quenched SF
Early
types
Grebel: Star Formation in Different Galaxy Types
HI Consumption
Time Scale
(M(HI)/SFR)
! With increasing
luminosity, HI content drops off faster
than SFR
$ Shorter HI consumpt.
time scales.
20
Late
types
Hubble
time
Bothwell et al. 2009,
MNRAS, 400,154
Early
types
! All gas consumption
times: > 100 Myr
$ & 1 dynamical time scale in a typical galaxy $ lower SFR limit.
! Gas mass / minimum gas assembly time: & free-fall collapse time.
$ SFR upper limit.
! Low-mass galaxies: Very low SFR and very extended HI disks
(very little of existing gas is available for star formation).
22.02.2013
Grebel: Star Formation in Different Galaxy Types
21
Hunter, Elmegreen
Irregulars: Random Gas Motions Dominate
% Star formation is occurring in clouds even where the average gas
column density is < Toomre 'c.
& Difference between dIm & spirals is context in which clouds form.
% 60–90% of HI is in cool HI filaments (both spirals and Im)
% Dwarfs may contain relatively more warm HI than spirals.
% Cool gas is more important in determining star formation.
% No correlation between cooler HI component and integrated star
formation rate observed in dwarfs.
& The immediate reservoir of gas for cloud formation may not be as
extensive as integrated HI mass would indicate.
% HII regions in dIms are overpressured relative to ambient
disk pressures by factor of 10 compared to spirals.
& Greater role possible for pressurized triggering and shell formation.
% ISM in Im galaxies: structured into clouds of all sizes (fractal) whose
distributions resemble those of compressible turbulence.
Grebel: Star Formation in Different Galaxy Types
22
Grebel & Brandner 1998, inThe Magellanic Clouds and Other Dwarf
Galaxies, eds. Richtler & Braun (Shaker Verlag), p. 151
22.02.2013
Spatial
Variations:
Recent Star
Formation
History of
the LMC
Long-lived regions of
active star formation
in irregular galaxies.
Life times a few 10 –
100 Myr.
Irregular appearance
dominated by young
HII regions.
Old populations fairly
smooth and homogeneous.
22.02.2013
Grebel: Star Formation in Different Galaxy Types
23
Magellanic Clouds: Old Populations
Old stars in the
Magellanic Clouds:
Sparse. Hard to find.
Traced best by using
RR Lyrae and other
HB stars. $ Overall
no gradients in
metallicity, but
large spread.
(Haschke et al. 2012,
AJ, 143, 48)
Most metal-poor LMC
star found so far:
[Fe/H] = –2.67.
Haschke et al. 2012, AJ, 144, 88
(["/Fe])old = 0.36.
Individual abundances
and trends resemble
dSphs and MW ((inner) halo accretion).
22.02.2013
Grebel: Star Formation in Different Galaxy Types
24
The SMC Cluster Age-Metallicity Relation
Kayser et al. 2008, Kayser PhD Thesis,
Glatt et al. 2008
VLT spectroscopy & ACS photometry of SMC clusters:
Metallicity spread at a given age; SMC not well mixed!
[Fe/H]CG97
Parisi et al. 08
NGC 330
Age [Gyr]
22.02.2013
Grebel: Star Formation in Different Galaxy Types
25
Dwarf Distance from Primary vs. HI Mass
`Galactic halo’
22.02.2013
Grebel: Star Formation in Different Galaxy Types
26
Metallicity-Luminosity. relation for the same (old) populations
dSphs
– 0.5
dIrrs; but also: evolution as independent entities!)
dSphs: too metal-rich
for their luminosity; even
allowing for evolution
([Fe/H])
–1
–1.5
–2
Here:
“error bars”
Indicate true
range of – 2.5
metallicities,
not uncertainty.
22.02.2013
dIrrs
dIrr/dSphs
dSphs
dEs
6
7
log Lbary [L!]
8
Grebel: Star Formation in Different Galaxy Types
9
27
Shetrone et al. 2001
Koch et al. 2010
Lower ["/Fe] @ [Fe/H] in dSphs than in Galactic halo:
! Low SFRs (little contribution from massive SNe II (")), or
! Loss of metals and SN ejecta by galactic winds, or
! Larger contribution from SNe Ia (Fe enhanced over ")
! Inefficient enrichment.
22.02.2013
Grebel: Star Formation in Different Galaxy Types
28
Abundance Inhomogeneities in Dwarfs
! Considerable abundance spreads observed in field stars:
! Up to > 1 dex even in dwarfs dominated by old popul.
(e.g., Shetrone et al. 2001, ApJ, 548, 592; Norris et al. 2008; ApJ, 689, L113)
! At a given age:
scatter in abundances
Carina
e.g., SMC (Glatt et al.
2008, AJ, 136, 1703),
Sex B (Kniazev et al.
2005, AJ, 130, 1558).
! At a given metallicity:
scatter in " abundance
ratios (e.g., Koch et al.
2008, AJ, 135, 1580)
( Slow, stochastic SF, low SFE
22.02.2013
[Fe/H]
Koch et al. 2008, AJ, 135, 1580
Grebel: Star Formation in Different Galaxy Types
29
Wide Range of Star Formation Histories Observed
Downsizing
High-mass regime:
% Very rapid, efficient early SF with strong enrichment.
% Mostly inactive today.
Intermediate-mass regime (MB < –19; M" > ~1010 M!)
% Early types: More activity in low-density environments.
% Late types: Continuous SF over a Hubble time,
well correlated with H2.
Low-mass regime (MB < –15; M" < ~108 M!)
% Wide variety of properties from bursting to quiescent.
% High amount of gas may not imply high SFR.
% Generally, stochasticity dominates; upper IMF sparsely sampled.
Often: low SFE, low SFR (exception: e.g., BCDs).
% Susceptibility to disturbances; environmental dependence.
22.02.2013
Grebel: Star Formation in Different Galaxy Types
30