X-ray Emission from
Primordial Starbursts
Antara Basu-Zych (NASA/GSFC & UMBC)
Ann Hornschemeier
Tassos Fragos
Bret Lehmer
Andy Ptak
Panayiotis Tzanavaris
Mihoko Yukita
Andreas Zezas
X-ray Emission from Primordial Starbursts
X-ray emission in galaxies...
Active galactic nuclei (AGN):
Chandra image of M82
-- centrally located point source
-- accretion onto supermassive black hole
Hot Gas:
-- diffuse and spatially extended
-- contributes to the soft X-ray band (0.5-2 keV)
X-ray Binaries:
0.3--1.1 keV
0.7--2.2 keV
2.2-6 keV
-unresolved point sources
-dominates in the hard X-ray band (2-8 keV)
- accretion onto compact objects
astronomynow.com
Low Mass X-ray Binaries (LMXBs)
Northwestern
High Mass X-ray Binaries (HMXBs)
• Lower-mass star (<1.5 M⊙) evolves
and swells to red giant feeding the
compact object.
• Massive O/B star (>8 M⊙) secondary
feeding a compact object (neutron star
or BH).
• Old stars (>1 Gyr) - trace starformation history and stellar mass of
the galaxy.
• Massive/short-lived (~10−30 Myr) trace recent star-formation.
X-ray Binaries in Nearby Galaxies: Local Scaling Relations
α = (9.05 ± 0.37) × 1028 erg s−1 M⊙−1
β = (1.62 ± 0.22) × 1039 erg s−1 (M⊙ yr−1)−1
Colbert et al. (2004)
Iwasawa et al. (2009)
Lehmer et al. (2010)
Northwestern
LX ∝ SFR0.7
LX ∝ SFR0.9
Scatter ~ 0.5 dex
Scatter ~ 0.3 dex
High Mass X-ray Binaries (HMXBs)
• To first-order, a physically-motivated scaling of LX will include both SFR and
M★ to account for HMXBs and LMXBs:
LX = LX(LMXBs)+LX(HMXBs) = α M★ + βSFR ⇒ LX/SFR = α (SFR/M★)-1 + β
X-ray Emission from Primordial Starbursts
Why do we care?
What does this mean?
Primordial Mode of Star Formation:
• dominated by recent star formation: high SFR/M★
• less chemically evolved: lower metallicities
• and less dust attenuation
… compared to present-day (z=0) galaxies.
z=0 Luminous IR
galaxies
z=0
LIR/LFUV
SDSS local star-forming galaxies
(contours)
Normal z=0
star-forming
galaxies
z=2 galaxies
z=2
(Erb et al, 2006)
109
Overzier et al, 2010
(Reddy et al, 2010)
SCREAME
D THE
DUST
SPECK
Overzier et al, 2011
1010
L
bol
1011
=L
IR
+L
1012
UV
1013
=SFR
X-ray Emission from Primordial Starbursts
Why do we care?
What does this mean?
• X-ray binary formation and evolution
(White & Ghosh, 1998; Lehmer+2010; Cowie+2011, BZ+2013; Fragos+2013a, Kaaret2014)
• Heating of the Intergalactic medium (IGM)
(Mesinger+2013; Fragos+2013b; Pacucci+2014)
• Superwinds
(Strickland+2004,2009; Yukita+2012)
z=0 Luminous IR
galaxies
z=0
LIR/LFUV
SDSS local star-forming galaxies
(contours)
Normal z=0
star-forming
galaxies
z=2 galaxies
(Reddy et al, 2010)
z=2
(Erb et al, 2006)
109
Overzier et al, 2010
Overzier et al, 2011
1010
L
bol
1011
=L
IR
+L
1012
1013
UV =SFR
X-ray Emission
from
Primordial Starbursts
Our
Focus:
Why
do we
care?
does over
thiscosmic
mean?
•X-rayWhat
binary evolution
time (driven by metallicity
evolution?)
using
Chandra
Deep Field-South data to study X-ray emission in galaxies between z=0—5
Primordial: galaxies from
the early Universe (z > 2)
X-ray• binary
populations
within individual, nearby (z < 0.1) analogs of high-z (z > 2) Lyman
high SFR
per stellar mass
lower dust(low
attenuations,
break•galaxies
metallicity, low dust attenuation)
• and lower metallicities
… compared to present-day
galaxies.
Lyman(z=0)
break
analogs, LBAs
•
z=0 Luminous IR
galaxies
z=0
LIR/LFUV
SDSS local star-forming galaxies
(contours)
Normal z=0
star-forming
galaxies
z=2 galaxies
(Reddy et al, 2010)
z=2
z~0.2
(Erb et al, 2006)
z~0.2
local analogs
local analogs
109
Overzier et al, 2010
Overzier et al, 2011
1010
1011
1012
1013
L
=L
+L
bol
IR
UV =SFR
Chandra Deep Field-South: Deepest X-ray View of the Universe!
4 Ms Chandra exposure
465 arcmin2
740 sources
Hubble Ultradeep Field (Beckwith et al. 2006)
Chandra Deep Field-South (Xue et al. 2011)
Chandra
We love you!
7 Ms CDF-S Observations
(additional
Ms) are almost
completed: data
Within the Chandra
Deep3Field-South,
the multiwavelength
(e.g., Hubble) have
revealed
are many
10s of thousands
Expect to Be Galaxy-Dominated
(vs.
AGN)there
in Most
Sensitive
Regions. of
galaxies
reaching
back
to when universe is <1 Gyr old!
(see Lehmer
et al.,
2012)
Deep-Field Galaxy Selection from Multiwavelength Data:
Lyman break galaxies
Hubble
Significance of LBGs:
•Efficient technique for discovering
high redshift (z>3) galaxies
•Trace cosmic star formation history
•Highest z galaxies? (possibly first
galaxies)
Chandra
Volume-averaged star formation rate for the Universe
VLA
VLT
Spitzer
Herschel
• Excellent sample for studying the
average X-ray emission properties of
galaxies over cosmic time
z
instrument
NLBGS
referenceTgalaxies.
1.5
HST/WFC3
48
Oesch et al. (2010)
1.9
HST/WFC3
91
Oesch et al. (2010)
2.5
HST/WFC3
359
Oesch et al. (2010)
3.0
CTIO+HST/ACS
361
Lehmer et al. (2005)
3.8
HST/ACS
2098
Bouwens et al. (2007)
5.0
HST/ACS
445
Bouwens et al. (2007)
5.9
HST/ACS
181
Bouwens et al. (2007)
6.8
HST/ACS+WFC3
73
Bouwens et al. (2010)
8.0
HST/WFC3
60
Bouwens et al. (2010)
Does the local relation hold at higher redshifts?
Age of the Universe (Gyr)
13.5 9.0 6.7 5
4
3
2
Medium SFR
Stacked LBGS
Colbert et al (2004)
Iwasawa et al (2009)
Lehmer et al (2010)
Laird et al (2005)
Lehmer et al
(2010)
log LX/SFR (erg s-1 [M8 yr -1]-1)
High SFR
Stacked LBGS
0
Lehmer et al
(2008)
1
Laird et al (2006)
2
Redshift (z)
3
4
BZ+13
LBG samples binned by
Redshift and SFR:
z=1.5, 1.9, 2.5, 3.0, 4.0, 5.0, ...
How does Lx/SFR evolve over cosmic time?
(higher redshifts did not yield
detections...)
SFR/[M8yr-1]= 5 -15 & 15 -100
(<5 and >30 did not yield detections)
log LX =A log(1 + z ) + B log SFR + C
A = 0.93 +/- 0.07
B = 0.65 +/- 0.03
C = 39.80 +/- 0.03
(see also Cowie et al. 2011; Kaaret et al. (2014)
Models from Fragos et al. (2012)
Primordial Starbursts in our backyard
Studying the X-ray emission within individual low-metallicity, high SFR galaxies:
Sample of z~0.1 Lyman break analogs
UV-selected:
high SFRs, metal and dust poor
resemble LBGs:
metallicity, dust attenuations, SFRs, morphology, kinematics…
(Heckman+2005, Hoopes+2007, Basu-Zych+2007,2009a, 2009b, Overzier+2008,2010,2011, Goncalves+2001)
We use optical emission lines to
< 0.1 (LBAs) vs.
z > 1.5 (LBGs) AGN!
screenz against
selecting
study in better details -- better spatial resolution, fainter features
X-rays: study individual galaxies (vs. average properties)
J082355+280621
VV 114
Mrk 54
Haro 11
Studying X-ray emission within individual z < 0.1 LBAs
High SFR
Stacked LBGS
Basu-Zych et al. (2013)
Medium SFR
Stacked LBGS
LBAS
VV 114
Colbert et al (2004)
Iwasawa et al (2009)
Lehmer et al (2010)
Fragos et al. (2013b)
Haro 11
What drives the elevated X-ray/SFR in UV-selected galaxies?
Lower Metallicities?
Theory: HMXBs in low metallicity environments are
more luminous and UV-selected galaxies have lower
metallicities compared to other higher SFR galaxies
(LIRGs/ULIRGs).
Observation: Current constraints indicate a
negative correlation between LX/SFR and
metallicity at the 99.2% confidence level.
Studying X-ray emission within individual z < 0.1 LBAs
Basu-Zych et al. (2013)
NULX/SFR
Z/Z◉ < 10%
Mapelli et al.
(2010)
SINGS
VV 114
Prestwich et al. (2013)
Brorby et al. (2014)
Fragos et al. (2013b)
12+log(O/H)=7.65
Haro 11
Observational evidence suggests that the X-ray binary populations per unit SFR are more
luminous in low-metallicity galaxies (dwarfs and LBAs).
Distribution of X-ray binaries within spatially-resolved LBAs
Only the BRIGHT end of the luminosity distribution:
LX > 1040 erg/s (ULXs)
J082355+280621
5’’
Haro 11
VV 114
5’’
Contours:
Chandra X-ray data
2-10 keV
0.5-10 keV
Target
Exposure time
VV114
60 ks
Haro11
54 ks
J082355
9 ks
Distribution of X-ray binaries within spatially-resolved LBAs
Are the observed bright sources REALLY single ULXs?
OR the result of multiple blended sources?
Simulate the effects of source blending…
1. Draw random distributions ...
HST images:
Spatial distribution
Produce simulated 2--10 keV Chandra
images that match depth of actual
observations
Mineo et al. (2012) XLF:
HMXB luminosity distribution
5’’
2. Marx ray tracing code
VV 114
+
VV114
simulated
observed
Haro11
Haro 11
5’’
Distribution of X-ray binaries within spatially-resolved LBAs
Are the observed bright sources REALLY single ULXs?
OR the result of multiple blended sources?
Simulate the effects of source blending…
Basu-Zych et al. (2013)
Haro11
VV114
Mineo+
2012a
Fragos+2013
But include influence from metallicity this time!
Renormalize the input luminosity function by the
Lx/SFR enhancement due to low metallicity
Summary
& the exciting future...
Metallicity is an important factor for driving the formation and evolution of
HMXBs, based on three different investigations of “primordial starbursts”:
•X-ray stacking analyses for z < 4 LBGs (covering ∼90% of the universe’s
history) using the 4 Ms Chandra Deep Field South data
•Studies of individually-detected LBAs, with similarly low metallicities and
elevated LX/SFR as LBGs
•… and characterizing the bright end of the X-ray luminosity function within
spatially-resolved LBAs
Use upcoming Chandra Deep Field-South 7 Ms data
to take this study deeper!
Summary
Next steps...
Due to their uniquely low metallicities, low dust attenuations and high SFRs in
the local Universe, z~0.1 LBAs represent an important population for studying
X-ray emission within galaxies similar to those in the early Universe (in
primordial mode of star formation) & offer some advantages over studying
high-z samples:
• individually detected (vs. studying average properties)
• higher spatial resolution
NGC 3310
Mrk 54
J082355+280621
Building up a larger sample of
low metallicity & high SFR galaxies
• larger sample of LBAs
• with deeper observations on other spatially resolved LBAs
Summary
& the exciting future...
Due to their uniquely low metallicities, low dust attenuations and high SFRs in the
local Universe, z~0.1 LBAs represent an important population for studying X-ray
Athena
emission within galaxies similar to those in the early Universe & offer some
Simulatedover
spectrum
for high-z samples:
advantages
studying
Ne IX He α
triplet
25 ks with Athena XIFU
• Individually detected
• Less biased towards the brightest galaxies
• Higher spatial resolution
• Possibility of studying the hot gas contribution
FeXX, XXI
Based on the average X-ray spectrum for 21 local star-forming galaxies, the hot gas
component is well described by kT~ 0.3 keV (Mineo et al. 2012b)
Haro11
NOT accessible for z > 1 galaxies.
Thanks!
Conclusions
& Next steps...
•
Based on X-ray stacking analyses for z < 4 LBGs (covering ∼90% of the universe’s
history) using the 4Ms Chandra Deep Field South data, we find that the 2–10 keV X-ray
luminosity evolves weakly with redshift (z) and SFR as
log LX = 0.93 log(1 + z) + 0.65 log SFR + 39.80.
•
Consistent with predictions from X-ray binary population synthesis models, the redshift
evolution of LX/SFR appears to be largely driven by metallicity evolution in high mass Xray binaries.
•
Based on X-ray emission studies of individually-detected Lyman break analogs, which
have similarly low metallicities and elevated LX/SFR as high-z LBGs, we find that the
relatively metal-poor, active mode of star formation in LBAs and distant z > 2 LBGs may
yield higher total HMXB luminosity than found in typical galaxies in the local Universe.
•
Based on X-ray emission studies of individually detected Lyman break analogs, which have
similarly low metallicities and elevated LX/SFR as high-z LBGs, the relatively metal-poor,
active mode of star formation in LBAs and distant z > 2 LBGs may yield higher total HMXB
luminosity than found in typical galaxies in the local Universe.
UVLG : LFUV ≥ 2 x 1010 L
Lyman break analogs (LBAs) : IFUV ≥ 109 L kpc-2
LBGs/
LBAs
LBA Overview:
z ~0.1-0.3
rare (at z<1 = 10-5/Mpc3) but
dominate UV emission at z>3
compact : half light radii = 1-2
kpc)
high SFRs : 1-100 M⊙/yr
high sSFR: SFR/M⊙~10-9 - 10-8
Hoopes et al. (2007)
X-ray Emission from Primordial Starbursts
X-ray emission in galaxies...
Average X-ray spectrum for 21 local star-forming galaxies (Mineo et al. 2012a,b)
is described well by models of:
bremsstrahlung (hot gas; kT ~ 0.3 keV) plus power-law due to X-ray binaries (Γ ~ 1.8)
Chandra image of M82
0.5-2 keV
2-10 keV
Total Emission
X-ray Binaries
Hot Gas
Mineo et al. (2012a,b)
0.3--1.1 keV
0.7--2.2 keV
2.2-6 keV
At higher redshifts, the X-ray binary contribution dominates.
Chandra Deep Field-South: Deepest X-ray View of the Universe!
Lehmer et al. (2012)
S−1.5
S−2.2
• At 4 Ms depth, we estimate number
Ms Chandra exposure
counts4465
toarcmin
~5 ×
10−18 erg cm−2 s−1 (0.5−2
2
keV) 740
andsources
obtain source densities of
~28,000 deg−2.
• At the 0.5−2 keV flux limit, AGNs and
galaxies provide comparable contributions
to number counts:
AGNs − 14,900 deg−2 (560 sources)
galaxies − 12,700 deg−2 (170 sources)
Hubble Ultradeep Field (Beckwith et al. 2006)
Chandra
We love you!
7
• Relatively sharp slope of normal galaxy
counts (dN/dS ∝ S−2.2) indicate that we
Chandra Deep Field-South (Xuey et al. 2011)
will soon be in a galaxy dominated
regime.
Within the Chandra Deep Field-South, the multiwavelength data
(e.g., Hubble) have revealed there are many 10s of thousands of
Ms CDF-S Observations
(additional
Ms) areare
almost
completed:
galaxies, but
only ~1703galaxies
individually
detected by
Chandra.
Expect to Be Galaxy-Dominated in Most
Sensitive Regions.
Selecting Lyman break galaxies
Un
G
R
Color selection at
z=3:
(Un - G)  1+(G-R)
(Un -G)  1.6
(G-R)  1.2
Shapley et al, 2003
HMXBs detected in spatially-resolved LBAs
Target
Exposure time
Nulx (observed)
Nulx(expected)
VV114
60 ks
5
1.3
Haro11
54 ks
2
0.5
J082355
9 ks
~3-4
0.6
Haro 11:Using VLT XShooter data, knot C appears to be associated with
luminous blue variable stars Ages for Knots B and C are <10Myr
(Guseva+2012)
Summary
Implications...
-- Heating of the Intergalactic Medium -Based on three different investigations:
•X-ray stacking analyses for z < 4 LBGs (covering ∼90% of
the universe’s history) using the 4Ms Chandra Deep Field
South data
•Studies of individually-detected LBAs, with similarly low
metallicities and elevated LX/SFR as LBGs
•… and characterizing the bright end of the X-ray luminosity
function within spatially-resolved LBAs
we find that metallicity is an important factor driving the
formation and evolution of HMXBs within low-metallicity and
high SFR galaxies (“primordial
* First galaxies starbursts”).
at z=10-20
* XRBs dominate over AGN (Fragos+2013)
* Lx/SFR does not follow the local relation, but evolves with metallicity evolution of the
Universe, as predicted by XRB population synthesis models...
Average X-ray spectrum for 21 local star-forming galaxies (Mineo et al. 2012a,b)
is described well by models of:
bremsstrahlung (hot gas; kT ~ 0.3 keV) plus power-law due to X-ray binaries (Γ ~ 1.8)
0.5-2 keV
2-10 keV
Total Emission
X-ray Binaries
Hot Gas
At higher redshifts,
the X-ray binary
contribution
dominates, and hot
gas component is
not easy to study!
Mineo et al. (2012a,b)
At z=0, the hot gas component and XRB component are nearly equal at E=0.5-2keV
Next steps with Chandra 7 Ms Deep Field Data
Lehmer et al. in-prep
Based on three different investigations:
•X-ray stacking analyses for z < 4 LBGs (covering ∼90% of
the universe’s history) using the 4Ms Chandra Deep Field
South data
•Studies of individually-detected LBAs, with similarly low
metallicities and elevated LX/SFR as LBGs
•… and characterizing the bright end of the X-ray luminosity
function within spatially-resolved LBAs
we find that metallicity is an important factor driving the
formation and evolution of HMXBs within low-metallicity and
high SFR galaxies (“primordial starbursts”).
SFRs from IR and UV.
SFRs from extinctioncorrected UV only.