CHITALS: Cold HI 21-cm Absorption Line Survey
2015 PHISCC Workshop: HI Surveys Get Real
Rajeshwari Dutta
(with R. Srianand & Neeraj Gupta)
IUCAA
18 March, 2015
Rajeshwari Dutta (IUCAA)
CHITALS
18 March, 2015
1 / 17
Cold Gas in & around low-z Galaxies
Motivation: Understand CNM phase (T ∼ 100 K & n ∼ 1 cm−3 ) in ISM and
CGM of low-z galaxies, trace redshift evolution of CNM
Objective: Connect between H i 21-cm absorption and galaxy properties
Method: H i 21-cm absorption survey of Quasar-Galaxy-Pairs (QGPs)
Rajeshwari Dutta (IUCAA)
CHITALS
18 March, 2015
2 / 17
Low-z H i 21-cm absorption studies
21-cm absorption is an useful tool to study thermal state, parsec-scale
structure, filling factor of cold neutral gas in ISM & CGM
Nature of 21-cm absorption line systems still unclear (small number statistics,
pre-selection biases, origin of absorbers,...)
Low-z 21-cm absorption survey: detect associated galaxies, H i 21-cm emission,
milliarcsecond-scale VLBI spectroscopy
Rajeshwari Dutta (IUCAA)
CHITALS
18 March, 2015
3 / 17
Quasar Galaxy Pairs
QGPs to probe cold gas in/around galaxies: Carilli & van Gorkom 1992, Gupta+
2010, Borthakur+ 2011
Carilli & van Gorkom 1992
Rajeshwari Dutta (IUCAA)
Gupta+2010
CHITALS
18 March, 2015
4 / 17
Sample Construction
Largest sample of low-z QGPs (∼100):
Cross-matching:
FIRST (S(1.4GHz) > 50 mJy)
SDSS-DR10 galaxies (zgal(phot) < 0.4)
Galaxy on top of QSO
Rajeshwari Dutta (IUCAA)
CHITALS
18 March, 2015
5 / 17
Sample Construction
Largest sample of low-z QGPs (∼100):
Cross-matching:
FIRST (S(1.4GHz) > 50 mJy)
SDSS-DR10 galaxies (zgal(phot) < 0.4)
Galaxy on top of QSO
Sub-sample of 46 QGPs at b ≤ 40 kpc (largest
absorption-unbiased sample of low-z galaxies)
Gupta+ 2013
Rajeshwari Dutta (IUCAA)
CHITALS
18 March, 2015
5 / 17
Observations
Optical:
SDSS-DR10
SALT long-slit spectra (∼50 hrs)
Galaxy z, SFR, stellar mass, virial radius & metallicity
Radio:
GMRT & VLA L-band (∼250
R hrs)
3σ optical depth sensitivity τ dv ∼ 0.1 km s−1 (dv = 5 km s−1 )
Spectral resolution ∼ 2 km s−1
Spectral coverage ∼ 1000 km s−1
Rajeshwari Dutta (IUCAA)
CHITALS
18 March, 2015
6 / 17
SALT Spectra
J1254+0546 zgal=0.0246
J1457+0519 zgal=0.2198
8
8
J125422.19+054619.8
6
6
Normalised Flux
Normalised Flux
J145722.53+051921.8
4
J145722.40+051918.8
2
4
2
J125422.21+054610.4
0
6650
0
6700
6750
6800
6850
Observed Wavelength (Å)
6900
6950
8000
8050
J1133+0015 zgal=0.0752, 0.0758
J155121.13+071357.7
Normalised Flux
3
Normalised Flux
8200
8250
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
4700
4710
4720
2
4730
4740
Observed Wavelength (Å)
4750
4760
4770
1.1
1.0
1
J113302.01+001541.7
J155121.06+071352.4
0
7030
Rajeshwari Dutta (IUCAA)
7040
7050
7060
7070
Observed Wavelength (Å)
7080
7090
7100
CHITALS
Normalised Flux
J113303.02+001549.0
8100
8150
Observed Wavelength (Å)
J1551+0713 zgal=0.1007
4
0.9
0.8
0.7
0.6
0.5
0.4
6460
6470
6480
6490
Observed Wavelength (Å)
18 March, 2015
6500
6510
7 / 17
Probing ISM using multi-wavelength observations of QGP
Srianand+2013
Rajeshwari Dutta (IUCAA)
CHITALS
18 March, 2015
8 / 17
21-cm absorption from QGPs
Galaxy on top of QSO (b = 5 kpc): Ca ii, Na i and H i 21-cm absorption at z
= 0.1468
J143806.79+175805.4
Galaxy on top
Rajeshwari Dutta (IUCAA)
CHITALS
18 March, 2015
9 / 17
21-cm absorption from QGPs
Galaxy on top of QSO (b = 5 kpc): Ca ii, Na i and H i 21-cm absorption at z
= 0.1468
J143806.79+175805.4
Galaxy on top
fc N(H i) / Ts = 0.88 × 1019 cm−2 K−1
J1438+1758 21-cm absorption
SDSS
1.2
0.8
0.6
4500
4510
4520
4530
4540
Observed Wavelength (Å)
0.8
4550
4560
1.1
0.6
0.5
-40
Rajeshwari Dutta (IUCAA)
-20
0
20
Velocity Relative to zabs = 0.1468 (km s-1)
40
CHITALS
1.0
0.9
0.8
6740
6750
NaI λ5897
Normalised Flux
0.7
NaI λ5891
Normalised Flux
0.9
1.0
CaII λ3969
1.0
CaII λ3934
Normalised Flux
1.1
6760
Observed Wavelength (Å)
6770
6780
18 March, 2015
9 / 17
21-cm absorption from QGPs
Two galaxies along sightline: foreground at z = 0.1007 (no 21-cm absorption)
& background at z = 0.3291 (21-cm absorption)
J155121.13+071357.7
J155121.06+071352.4
Rajeshwari Dutta (IUCAA)
CHITALS
18 March, 2015
10 / 17
21-cm absorption from QGPs
Two galaxies along sightline: foreground at z = 0.1007 (no 21-cm absorption)
& background at z = 0.3291 (21-cm absorption)
J155121.13+071357.7
J155121.06+071352.4
fc N(H i) / Ts = 0.09 × 1019 cm−2 K−1
J1551+0713 21-cm absorption
SDSS
0.4
3710
MgII λ2803
0.6
0.2
3700
0.95
3720
Observed Wavelength (Å)
3730
3740
0.90
0.80
-40
Rajeshwari Dutta (IUCAA)
-20
0
20
Velocity Relative to zabs = 0.32892 (km s-1)
40
CHITALS
1.00
0.95
0.90
0.85
0.80
5200
5220
CaII λ3969
0.85
CaII λ3934
Normalised Flux
Normalised Flux
1.00
0.8
MgII λ2796
Normalised Flux
1.0
5240
5260
Observed Wavelength (Å)
5280
5300
18 March, 2015
10 / 17
21-cm absorption from QGPs
J004121.53-014257.0
J004126.01-014315.6
Rajeshwari Dutta (IUCAA)
CHITALS
18 March, 2015
11 / 17
21-cm absorption from QGPs
J004121.53-014257.0
J004126.01-014315.6
A z = 0.01767 spiral galaxy at b = 25 kpc from an extended radio-loud QSO
fc N(H i) / Ts = 0.12 × 1019 cm−2 K−1 for sightline A
To be reobserved for better constraining the galaxy H i emission and absorption
Rajeshwari Dutta (IUCAA)
CHITALS
18 March, 2015
11 / 17
A QGP with disparate H2 and 21-cm absorption
Both H2 and 21-cm absorption simultaneously for the first
time at z < 1 (Dutta+ 2015, MNRAS, 448, 3718)
Chen+ 2005
Rajeshwari Dutta (IUCAA)
CHITALS
18 March, 2015
12 / 17
A QGP with disparate H2 and 21-cm absorption
Both H2 and 21-cm absorption simultaneously for the first
time at z < 1 (Dutta+ 2015, MNRAS, 448, 3718)
Chen+ 2005
Sub-DLA at z = 0.10115 shows strong H2 , C i and Na i absorption from one of the
two components in HST/COS spectrum
1.2
1.0
0.8
0.6
0.4
0.2
0.0
1.2
1.0
1.0
0.8
0.8
0.6
0.6
Normalised Flux
Normalised Flux
-0.2
1.2
0.4
0.2
0.0
-0.2
1.2
1.0
0.4
0.2
0.0
-0.2
1.2
1.0
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
0.0
0.0
-0.2
-100 -80
-0.2
-100
-50
0
50
-100
-50
0
50
-100
-50
0
50
-100
-50
0
50
-60
-40
-20
0
20
40 -100 -80
-60
-40
-20
Velocity Relative to zabs = 0.10115 (km/s)
0
20
40
Velocity Relative to zabs = 0.10115 (km/s)
Rajeshwari Dutta (IUCAA)
CHITALS
18 March, 2015
12 / 17
A QGP with disparate H2 and 21-cm absorption
Both H2 and 21-cm absorption simultaneously for the first
time at z < 1 (Dutta+ 2015, MNRAS, 448, 3718)
Chen+ 2005
Sub-DLA at z = 0.10115 shows strong H2 , C i and Na i absorption from one of the
two components in HST/COS spectrum
1.2
1.0
0.8
0.6
0.4
0.2
0.0
1.2
1.0
1.0
0.8
0.8
0.6
0.6
Normalised Flux
Normalised Flux
-0.2
1.2
0.4
0.2
0.0
-0.2
1.2
1.0
0.4
0.2
0.0
-0.2
1.2
1.0
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
0.0
0.0
-0.2
-100 -80
-0.2
-100
-50
0
50
-100
-50
0
50
-100
-50
0
50
-100
-50
0
50
-60
-40
-20
0
20
40 -100 -80
-60
-40
-20
Velocity Relative to zabs = 0.10115 (km/s)
0
20
40
Velocity Relative to zabs = 0.10115 (km/s)
Strong H2 component shows log N(H2 ) = 16.61 ± 0.05 and T01 = 133+33
−22 K
(Muzahid+ 2015)
Rajeshwari Dutta (IUCAA)
CHITALS
18 March, 2015
12 / 17
A QGP with disparate H2 and 21-cm absorption
N(H i) = 1.8 × 1018 Ts /fc
Z
τ dv (cm−2 )
Muzahid+ 2015
Rajeshwari Dutta (IUCAA)
CHITALS
18 March, 2015
13 / 17
A QGP with disparate H2 and 21-cm absorption
N(H i) = 1.8 × 1018 Ts /fc
Z
τ dv (cm−2 )
50
Muzahid+ 2015
40
30
MilliArc seconds
20
Our VLBA 1.4 GHz continuum image
contains only 27% of arcsecond scale
emission, extending over ∼131 pc at
redshift of absorber
10
0
-10
-20
-30
-40
-50
40
Rajeshwari Dutta (IUCAA)
CHITALS
20
0
MilliArc seconds
-20
-40
18 March, 2015
13 / 17
A QGP with disparate H2 and 21-cm absorption
Searched for 21-cm absorption and emission by Kanekar+ 2001 using ATCA
(M(H i) ≤ 2 × 109 M )
Rajeshwari Dutta (IUCAA)
CHITALS
18 March, 2015
14 / 17
A QGP with disparate H2 and 21-cm absorption
Searched for 21-cm absorption and emission by Kanekar+ 2001 using ATCA
(M(H i) ≤ 2 × 109 M )
No 21-cm absorption associated with the strong H2 component → either the
N(H i) associated with this component is ≤50% of the total N(H i) or the gas
covering factor is ≤ 0.27
Rajeshwari Dutta (IUCAA)
CHITALS
18 March, 2015
14 / 17
A QGP with disparate H2 and 21-cm absorption
Searched for 21-cm absorption and emission by Kanekar+ 2001 using ATCA
(M(H i) ≤ 2 × 109 M )
No 21-cm absorption associated with the strong H2 component → either the
N(H i) associated with this component is ≤50% of the total N(H i) or the gas
covering factor is ≤ 0.27
Weak tentative 3σ 21-cm absorption coincident with the weaker H2 component
→ spin temperature of ≤ 90 K, at odds with the weakness of H2 , C i and Na i
absorption in this component
Rajeshwari Dutta (IUCAA)
CHITALS
18 March, 2015
14 / 17
A QGP with disparate H2 and 21-cm absorption
Searched for 21-cm absorption and emission by Kanekar+ 2001 using ATCA
(M(H i) ≤ 2 × 109 M )
No 21-cm absorption associated with the strong H2 component → either the
N(H i) associated with this component is ≤50% of the total N(H i) or the gas
covering factor is ≤ 0.27
Weak tentative 3σ 21-cm absorption coincident with the weaker H2 component
→ spin temperature of ≤ 90 K, at odds with the weakness of H2 , C i and Na i
absorption in this component
25 hrs in VLA to obtain 3 times higher S/N and resolution 21-cm absorption
spectrum
Rajeshwari Dutta (IUCAA)
CHITALS
18 March, 2015
14 / 17
Sample of CHITALS
Low-z galaxies (z ≤ 0.4, median z = 0.1) with b ≤ 40 kpc and median b = 15
kpc → probe gas in optical disks of galaxies, extended H i disks, extraplanar or
intra-group gas
Ngal
8
6
4
2
0
40
b (kpc)
30
20
10
0
0.0
Rajeshwari Dutta (IUCAA)
0.1
0.2
zgal
0.3
0.4
0 1 2 3 4 5 6
Ngal
CHITALS
18 March, 2015
15 / 17
Sample of CHITALS
Low-z galaxies (z ≤ 0.4, median z = 0.1) with b ≤ 40 kpc and median b = 15
kpc → probe gas in optical disks of galaxies, extended H i disks, extraplanar or
intra-group gas
Ngal
8
6
4
2
0
40
b (kpc)
30
20
10
0
0.0
0.1
0.2
zgal
0.3
0.4
0 1 2 3 4 5 6
Ngal
Wide range of galaxy luminosity and morphology (early- to late-type), with
SDSS colour 1.0 ≤ u − r ≤ 5.0 and median u − r = 2 → important resource for
understanding high-z galaxy evolution based on absorption line studies
6
5
Ngal
4
3
2
1
0
1
2
3
4
5
u−r
Rajeshwari Dutta (IUCAA)
CHITALS
18 March, 2015
15 / 17
Summary & Upcoming Results
CHITALS will be an unbiased systematic survey of 21-cm absorption from the
largest sample of low-z galaxies
H i 21-cm optical depth around low-z galaxies as function of stellar mass, virial
radius and SFR
Application to high-z 21-cm absorbers and future blind 21-cm absorption
surveys
8 QGPs with 21-cm absorption detection till now
Statistical results to follow
Future follow-ups: HST/COS UV spectroscopy, VLBI imaging and
spectroscopy
Rajeshwari Dutta (IUCAA)
CHITALS
18 March, 2015
16 / 17
Rajeshwari Dutta (IUCAA)
CHITALS
18 March, 2015
17 / 17