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The
Larg
e D
efic
it of
HM
XB E
mis
sion
from
the
Circ
umnu
clea
rSt
arbu
rst R
ing
in N
GC
755
2 an
d Lu
min
ous
Infr
ared
Gal
axie
sLa
cey
Wes
t,1Br
et L
ehm
er,1
Andr
ea P
rest
wic
h,2
Kris
ten
Gar
ofal
i,1R
afae
l Euf
rasi
o,1
Was
utep
Luan
gtip
,3Ti
m R
ober
ts,4
Andr
eas
Zeza
s21.
Uni
vers
ity o
f Ark
ansa
s –
2. “C
fA” 3
. Srin
akha
rinw
irotU
nive
rsity
–4.
Dur
ham
Uni
vers
ity INIT
IAL
RES
ULT
SA
ND
FUTU
RE
WO
RK
(1) I
ndiv
idua
l Cha
ndra
poin
t sou
rce
spec
tra a
ssoc
iate
d w
ith S
F kn
ots
(Fig
. 1) a
re fi
t wel
l by
two-
tem
pera
ture
hot
gas
pl
us s
teep
pow
er-la
w m
odel
com
pone
nts,
con
sist
ent w
ith e
xpec
tatio
ns fo
r a p
opul
atio
n of
XR
Bs (F
ig. 3
). Pa
ram
eter
s ar
e no
t tig
htly
con
stra
ined
by
this
dat
a se
t, so
we
will
use
addi
tiona
l Cha
ndra
obse
rvat
ions
and
our
ne
wly
-obt
aine
d N
uSTA
Rda
ta to
bet
ter c
onst
rain
the
mod
els.
(2) P
relim
inar
y an
alys
is o
f new
ly-o
btai
ned
NuS
TAR
data
is c
onsi
sten
t with
pre
dict
ions
for a
circ
umnu
clea
rreg
ion
that
is d
efic
ient
in X
RB
s gi
ven
its m
easu
red
SFR
, and
inco
nsis
tent
with
exp
ecta
tions
for a
bur
ied
popu
latio
n of
XR
Bs (F
ig. 2
).
(3) W
e w
ill us
e ob
serv
ed X
-ray
lum
inos
ities
(or u
pper
lim
its) d
eriv
ed fr
om C
hand
ra a
t the
loca
tion
of e
ach
star
-fo
rmin
g kn
ot, a
long
with
SFR
val
ues
at e
ach
loca
tion
(Bra
ndl e
t al.
2012
) to
com
pare
the
L X–
SFR
for e
ach
knot
w
ith th
e L X
(HM
XB)–
SFR
rela
tion
from
Leh
mer
et a
l. 20
19 fo
r sta
r-for
min
g ga
laxi
es. O
ur p
relim
inar
y an
alys
is o
f the
C
hand
raan
d N
uSTA
Rda
ta s
ugge
sts
that
mos
t of t
he k
nots
will
be in
cons
iste
nt w
ith th
e Le
hmer
et a
l. 20
19 re
latio
n,
likel
y du
e to
ver
y yo
ung
ages
(≲5
Myr
) and
/or h
igh
met
allic
ity (>
1.5
Z ⊙)
Figu
re 2
: Im
ages
of N
GC
755
2 fro
m (l
eft)
Cha
ndra
in th
e 2-
7 ke
V b
and
and
(rig
ht)
NuS
TAR
in th
e 12
-25
keV
ban
d. If
the
star
-form
ing
regi
on is
def
icie
nt in
XR
Bs,
we
wou
ld e
xpec
t 45
sour
ce c
ount
s an
d 17
8 ba
ckgr
ound
cou
nts
in th
e10-
20 k
eV b
and
from
ex
trapo
latin
g th
e C
hand
rada
ta. W
e m
easu
re 4
0.5
sour
ce a
nd 1
67.5
bac
kgro
und
coun
ts in
the
12-2
5 ke
V N
uSTA
Rda
ta, i
ndic
atin
g th
at th
ere
is n
o bu
ried
XR
B
popu
latio
n an
d th
at th
e re
gion
is d
efic
ient
in X
RB
s gi
ven
its m
easu
red
SFR
.
AB
STR
AC
TLu
min
ous
infra
red
gala
xies
(LIR
Gs)
, the
mos
t ext
rem
e st
ar-fo
rmin
g ga
laxi
es in
the
near
by (D
< 3
0 M
pc)
Uni
vers
e, s
how
a n
otab
le X
-ray
emis
sion
def
icie
ncy
(up
to a
fact
or o
f ~10
) com
pare
d w
ith p
redi
ctio
ns
from
sca
lings
of th
e hi
gh m
ass
X-ra
y bi
nary
(HM
XB) l
umin
osity
func
tion
with
sta
r-for
mat
ion
rate
. In
the
near
by (≈
20 M
pc) L
IRG
NG
C 7
552,
the
maj
ority
of t
he IR
em
issi
on o
rigin
ates
in a
circ
um-n
ucle
ar
star
burs
t rin
g, w
hich
has
bee
n re
solv
ed in
to s
ever
al d
iscr
ete
knot
s of
sta
r for
mat
ion.
We
pres
ent r
esul
ts
from
rece
nt C
hand
raob
serv
atio
ns o
f NG
C 7
552,
whi
ch re
veal
a m
ajor
def
icit
in th
e 2-
7 ke
V X-
ray
emis
sion
from
two
of th
e th
ree
mos
t pow
erfu
l sta
r-for
min
g kn
ots.
The
lum
inou
s H
MXB
pop
ulat
ions
in
thes
e kn
ots
are
thou
ght t
o be
eith
er (1
) mis
sing
due
to re
lativ
ely
high
met
allic
ity a
nd/o
r you
ng a
ges
in
thes
e kn
ots
or (2
) obs
cure
d by
a v
ery
larg
e co
lum
n de
nsity
. We
aim
to d
istin
guis
h be
twee
n th
ese
poss
ibilit
ies
with
dat
a fro
m v
ery
rece
nt N
uSTA
Rob
serv
atio
ns, w
hose
sen
sitiv
ity a
bove
10
keV
is
expe
cted
to u
ncov
er a
ny o
bscu
red
HM
XB p
opul
atio
n, s
ince
em
issi
on a
t the
se e
nerg
ies
is m
ore
imm
une
to a
bsor
ptio
n ef
fect
s.
Figu
re 3
: Fits
to C
hand
ra 0
.3-7
keV
spe
ctra
. Sou
rce
and
back
grou
nd m
odel
s fit
sim
ulta
neou
sly
to u
nbin
ned
spec
tra in
XS
PE
C.
Spe
ctra
ext
ract
ed fr
om th
e (le
ft) n
orth
ern
poin
t sou
rce,
(cen
ter)
sou
ther
n po
int s
ourc
e, a
nd (r
ight
) ent
ire n
ucle
ar re
gion
. Poi
nt
sour
ce s
pect
ra a
re fi
t wel
l by
two-
tem
pera
ture
(T ~
0.3
and
0.8
keV
) hot
gas
plu
s po
wer
-law
mod
els.
Alth
ough
not
tigh
tly
cons
train
ed, t
he d
ata
appe
ars
to p
refe
r a s
teep
pow
er-la
w s
lope
(Γ~
2.2-
2.3)
in b
oth
case
s. S
pect
ra b
inne
d fo
r plo
tting
pu
rpos
es o
nly.
Cha
ndra
bac
kgro
und
mod
el d
evel
oped
follo
win
g B
arta
lucc
iet a
l. 20
14.
Figu
re 1
: (Le
ft) C
arne
gie-
Irvin
e B
VR
imag
e of
NG
C 7
552,
(cen
ter)
“zoo
med
-in” V
LT V
ISIR
imag
e of
the
[Ne
II]-e
mitt
ing
star
-form
ing
knot
s, a
s de
fined
by
Bra
ndl e
t al.
(201
2), a
nd (r
ight
) Cha
ndra
2–7
keV
imag
e of
the
sam
e ”z
oom
ed-in
” reg
ion,
with
kno
t loc
atio
ns la
bele
d. T
he m
ost
pow
erfu
l sta
r-for
min
g kn
ots
(M1
and
M2)
sho
w m
ajor
def
icits
in th
eir X
-ray
em
issi
on fo
r the
ir S
FRs.
We
seek
to d
eter
min
e w
ith N
uSTA
Rw
heth
er th
is p
opul
atio
n is
bur
ied
behi
nd a
ver
y la
rge
obsc
urin
g co
lum
n or
if th
e po
pula
tion
is s
impl
y no
t pre
sent
due
to a
ge a
nd/o
r m
etal
licity
effe
cts.
Figu
re 4
: We
will
use
obs
erve
d X
-ray
lum
inos
ities
(or u
pper
lim
its)
deriv
ed fr
om C
hand
raat
the
loca
tion
of e
ach
star
-form
ing
knot
, al
ong
with
SFR
val
ues
at e
ach
loca
tion
(Bra
ndl e
t al.
2012
) to
com
pare
the
L X –
SFR
for e
ach
knot
with
the
L X(H
MX
B)–
SFR
re
latio
n fro
m L
ehm
er e
t al.
2019
for s
tar-f
orm
ing
gala
xies
, sho
wn
abov
e. B
ased
on
our i
nitia
l ana
lysi
s, w
e ex
pect
mos
t of t
he k
nots
w
ill n
ot b
e co
nsis
tent
with
this
rela
tion,
like
ly d
ue to
age
/met
allic
ity
effe
cts.
Ack
now
ledg
emen
ts
We
ackn
owle
dge
supp
ortf
rom
the
Futu
reIn
vest
igat
ors
inN
ASA
Earth
and
Spac
eSc
ienc
e(F
INES
ST)
prog
ram
,th
eU
nive
rsity
ofAr
kans
asD
istin
guis
hed
Doc
tora
lFe
llow
ship
,C
XCgr
antG
08-1
9039
X,an
dN
ASA
gran
t80N
SSC
20K0
030.
This
wor
km
ade
use
ofda
tafro
mth
eC
hand
raX-
ray
Obs
erva
tory
and
from
the
Nuc
lear
Spec
trosc
opic
Tele
scop
eAr
ray
(NuS
TAR
)m
issi
on.W
eth
ank
the
Cha
ndra
and
NuS
TAR
team
sfo
rsup
port
with
exec
utio
nan
dan
alys
isof
thes
eob
serv
atio
ns.
1arcmin
SF K
not M
4SF
Kno
t M7
