1. CCAT Studies of Nearby Galaxies
Gordon Stacey and Shardha Jogee

2. CCAT: The Nearby Universe
Starforming galaxies
Continuum studies
Spectral line studies
Examples
Active galactic nuclei: revealing the torus
Surveys
Discussion of Galactic Center?
Discussion of modest z FS lines?

3. Motivation Extinction – we need to be able to observe the sources
Stars form in the dusty cores of molecular clouds so that probes of starformation are limited to the longer wavelength bands
Galactic nuclei are often enshrouded by many magnitudes of extinction, e.g. the Galactic Center suffers 28 magnitudes!
Cooling power – clouds need to cool to collapse and form stars
The starlight from newly formed stars is absorbed locally by interstellar dust, and reradiated in the far-IR and submillimeter bands
The Milky Way releases about half of its light in these bands
Starbursters and ULIGs emit most (up to 99%) of their light there
The primary cooling lines for the neutral ISM lie in the far-IR and submillimeter bands
Probes of the ISM – what is the effect of energy sources on the ISM…
Submillimeter lines trace the physical conditions (T,n,N…) of the gas, is it cooling to form stars, or being dissipated by starlight?
What are the effects of the interstellar radiation field on the ISM?
What are the effects of bars, spiral arm potentials and cloud-cloud collisions on the ISM?

4. The Extragalactic Niche
Low surface brightness in the short submm (200, 230, 350, and 450 um) windows:
It can be shown that the Atacama 25 m telescope is competitive per beam with any other terrestrial telescope existing or planned at these wavelengths
This is especially true for continuum work --
Extragalactic work requires modest resolving powers: R = / ~ 1000 to 10,000, or v ~ 300 to 30 km s-1
This can be achieved with direct detection spectrometers  significant sensitivity advantages possible
Nearby galaxies are extended  multiple beam systems are desirable
At present, large format spectrometers are easier to implement with direct detection systems.

5. Continuum Observations of Galaxies
The far-IR continuum emission from galaxies traces the deposition of optical starlight from nearby OB stars, or the diffuse ISRF
Traces regions of star formation in an extinction free manner.
Dust that peaks at 200 um is quite cold T ~ 20 K – trace the luminosity and mass of cold dust
For warmer dust, the submm colors are insensitive to T, since we are typically in the Rayleigh-Jeans tail.
However the warm dust properties are constrained by examining the apparent emissivity law.
Temperature and emissivity law yield dust column (mass)
Combined with shorter wavelength observations, we get the far-IR luminosity of the galaxy e.g. 38 or 60 um SOFIA or 70 um Spitzer observations, for which beam = 3.8”, 6”, and 20” respectively.

6. Continuum Observations
Visible
IRAS
ISO 175 m
The far-IR and visible morphologies of galaxies may often be quite different
IRAS and ISO imaging of the (optically) Sb galaxy M31 reveal a ring of cool dust – no spiral pattern is visible
There is also warm dust (star formation) in the nucleus
M31: Haas et al. 1998

7. Continuum Observations of M31
Most of the dust has a temperature of only 16 K – much cooler than inferred from IRAS data
The warm dust/cool dust ratio varies little across the galaxy  evidence for distinct dust populations
Cold dust mass ~ 3  107 M ten times greater than that inferred from IRAS data alone!
New dust mass, even if distributed uniformly would make the disk of M31 moderately opaque in the visible (AV ~ 0.5)

8. Far-IR Continuum: Revealing the Starburst
Charmandaris, Stacey and Gull 2002)
For IR luminous galaxies, the submm continuum (esp. together with far-IR continuum) traces the far-IR luminosity in an extinction free manner so it reveals the locations and luminosity of the starburst
For example, in the Arp 299 interacting system, components “B” (NCG 3690 nucleus) and “C” (overlap) appear equally important with “A” (IC 694 nucleus) at even mid-IR wavelengths.
However, at 38 um the continuum traces reveals that most (~ 75%) of the emission arises in the nucleus of IC 694!

9. Spectral Lines: the COBE FIRAS Spectrum of the Galaxy
[CII] line is strongest cooling line from Galaxy (L ~ 6 107 L)
Cools molecular cloud surfaces,atomic clouds, and HII regions
[NII] ~ 1/6 and 1/10 as bright as [CII]
Important coolants for low density ionized gas
Line ratio yields ionized gas density.
[NII] 3P1-3P0 (205 m) line has same density dependence as [CII] for ionized gas  constrains fraction of [CII] from ionized medium
For density bounded HII regions, the [NII] lines probe the ionizing photon rates: NLyman continuum

10. Neutral lines from the Galaxy
CO rotational transitions up to J = 8-7 detected
Strength of mid-J lines indicates substantial amounts of warm (T> 40 K), dense gas
Gas is particularly high excitation in the inner regions of the Galaxy
It is clear that the CO cooling power on a galactic scale arises in the submm bands
The submm [CI] lines are ubiquitous
Line ratio is near unity, temperature sensitive
 Tgas ~ 40 K
The combined cooling in the 370 and 610 um lines equals the total cooling in all of the CO lines
CO Rotational Diagram
Galaxy
Galactic Center
Submm Band
4-3
6-5
7-6

11. Unique Spectral Lines Available to CCAT
Species
Transition
E.P.1
 (m)
A (s-1)
ncrit (cm-3)2 N+
3P1  3P0 70
2.1  10-4
4.8  101 C0
3P2  3P1 63 24
2.7  10-7
7.9  10-8
1.2  103
4.7  102
12CO
13CO
J = 1312
J = 1110
J = 7  6
J = 6  5
503
430
155
116
111
2.4  10-4
1.6  10-4
3.6  10-5
2.2  10-5
2.0  10-5
5.6  106
3.7  106
3.9  105
2.6  105
2.3  105
1Excitation potential, energy (K) of upper level above ground.
2CO: Collision partner H2 (100 K). [CI]: H & H2, [NII]: e-.
Critical Densities, Energy above ground ensure:
Important astrophysical probes of ionized gas, molecular clouds, photodissociation regions, shocked regions, and astro-chemistry
Important cooling lines for much of the ISM

12. Molecular Lines in the Submm Telluric Windows
The CO molecule is often the dominant molecular gas coolant
The run of CO intensity (including isotopic lines) with J constrains T, n, and mass
It is the molecular gas reservoir that constrains future episodes of starformation
Low-J 12CO and isotopic CO lines cool the cold cores of molecular clouds and trace molecular cloud mass
Mid-J CO line emission signals the presence of PDRs associated with newly formed OB stars
High J CO line emission  molecular shocks, e.g. the warm molecular outflows associated with OB starformation, or cloud-cloud shocks formed in spiral density waves

13. The [CI] and CO(7-6) Lines
[CI] line ratio gives Tgas
Run of CO line intensity with J constrains molecular gas pressure
The CO(7- 6) and [CI] 3P2-3P1 (370 m) lines are only 1000 km s-1 (2.7 GHz) apart – easily contained in one extragalactic spectrum 
Excellent relative calibration
“Perfect” spatial registration
This line ratio of particular interest, as it is very density sensitive
CO(7-6)/[CI] 370 m line intensity ratio vs. density for various values for the strength of the ISRF (Kaufman et al. 1999)

14. Submm Line Observations: The [CI] and mid-J CO Lines
The CO(6-5) line first reported from a few starburst nuclei in 1991 (Harris et al. 1991)
Run of CO line intensity with J constrains molecular gas conditions
Gas is both warm, and dense – modeling was fit into a PDR (stellar UV heating) scenario
Since then, several galaxies have been detected, and many mapped in the lower J [CI] (610 um) line:
The [CI] line intensity traces Co column (high T, high n limit)
The [CI] line is an excellent tracer of molecular clouds in galaxies, perhaps better than CO (Gerin and Phillips, 1999)
The combined cooling in the [CI] lines is comparable to the CO line cooling – most (85%) of this is in the 370 um line.
There is a very high Co/CO abundance ratio (~ 0.5) in these galaxies – much higher than Milky Way values. This is either due to:
Fractionally more photodissociated gas due to cloud fragmentation
More Co produced molecular cloud interiors due to chemical processes associated with high cosmic ray fluxes or non-equilibrium chemistry

15. Starburst Galaxies: Mid-J CO
SPIFI CO(7-6) mapping of NGC 253 shows emission is extended over 500 pc region
Most of 2-5  107 M nuclear molecular gas is in a single highly excited component:
n(H2)~ 4.5  104 cm-3, T = 120 K
Consistent with CO and 13CO and H2 rotational line emission
This warm molecular gas is 10 to 30 times PDR gas mass (traced by [CII] & [OI] lines)
PDR scenarios fail to account for heating of this much molecular gas
 CO is heated by cosmic rays (~ 800  MW value) from the nuclear starburst.
Also provides a natural mechanism for heating the entire volume of gas
Bradford et al. 2003, ApJ 586, 891

16. Starburst Galaxies: Mid-J CO and [CI] 370 um Lines
[CI] and CO(76) lines simultaneously mapped from NGC 253:
The [CI]/CO(76) ~ 2/3  n > 3  104 cm-3 – consistent with our CO model
The [CI] (370 um)/(610 um) line ratio (~ 2) is sensitive to gas temperature, and yields Tgas>100 K – consistent with our CO model
From distribution and physical conditions, C0 and CO well mixed
 Cosmic ray enhancement of C0 abundance (cf. Farquhar, et al. 1994)
Consistent with our CO model  the primary heating source is cosmic rays from SN in starburst
SPIFI-JCMT [CI] 371 um & CO(76) (372 um) spectrum of the NGC 253 nucleus
[CI]
CO(76)
TMB = 1 K
Added heat at cloud cores will inhibit cloud collapse – halting starburst
Nikola et al. 2005

17. Example: Submm lines reveal the starburst in Arp 244
Simultaneous maps in the CO(7-6) and [CI] 370 m fine structure lines are possible since they lie only 1000 km s-1 apart
The relative line intensity calibration excellent
The easily excited [CI] line is ubiquitous
Mid-J CO line is much higher excitation
The CO/[CI] line ratio is very density sensitive
Strong mid-J CO line emission signals starformation

18. CO(7-6) and [CI] from the Antennae Galaxy
[CI] line constant and ubiquitous, it cools the overall ISM
CO(7  6) greatly enhanced at the starburst interaction zone reflecting the high gas excitation there
Strong mid-J CO emission reflects influence of OB stars
21” region
[CI] CO(7-6)
TMB = 100 mK
30” region
[CI] CO(7-6)
TMB = 50 mK
Interaction Zone
[CI] CO(7-6)
TMB = 200 mK
Isaak et al. 2005

19. Bars, Spiral Arms, and Starformation: M83
ISO: [OIII] 88 m
ISO: [NII] 122 m
ISO: [CII] 158 m
Nearby galaxies are easily imaged in the [NII], [CI] and mid-J CO lines
Spiral arms/inter-arm contrast highest for [OIII] 88 m line  earliest type stars (star formation) reside in the spiral arms
At bar/spiral arm interfaces, [OI], [CII], & [OIII] strongly enhanced  greatly enhanced starformation activity similar to Orion interface region 0.2 pc from 1C! Expect strong mid-J CO line emission there.
The SW bar region strong in H and CO as well (e.g. Kenney & Lord, 1991)  Orbit crowding likely triggers a massive burst of starformation

20. Bars, Spiral Arms, and Starformation: M83
3” [CI] beam  70 pc
ISO: [OIII] 88 m
6” Resolution CO (1-0) Map on false-color HI (Rand Lord, & Higdon 1999)
KAO Map in [CII] 55” Beam (Geis et al.)
Can easily resolve the far-IR continuum, ionized gas ([NII]), atomic/molecular gas [CI] and dense molecular gas (mid-J CO) as they cross the spiral arms – can we trace the compression and “ignition” of the next generation of stars?

21. Time to Map M83 Suppose we map M83 in the [CI] 370 m line:
Beam size ~ 3.7”, or 90 pc at 5 Mpc
Map eastern spiral arm: 2’  3’ region
Requires 800 pointings for sparse (single beam) sampled map
Predicted line flux is ~ 1  W-m2 in 3.7” beam
16 seconds of integration time yields SNR ~ 20
Total time for project: 7 hours seconds including a factor of 2 for overheads with a single pixel receiver!
Entire galaxy (35 square arcmin) takes 40 hours
A long slit spectrometer would reduce this time by the number of beams along the slit (probably ~ 32) so that the whole project will take only about an hour

22. Edge on Galaxies: NGC 891
2” beam 100 pc
Easy to image nearby edge-on galaxies in the lines and continuum tracers: Scale height of ISM – energetics -- super bubbles, chimneys
[NII] as extinction free, low excitation probe of ionized gas
[CI] traces atomic and/or molecular ISM
Regions of high mass star formation should appear in the mid-J CO lines
Far-IR continuum, star formation and cold dust
Scoville et al find CO(1-0) scale height ~ pc (4 to 6”) so that the galactic plane will be resolved.

23. CCAT and Active Galactic Nuclei
Galaxies for which a much of their
luminosity is not derived from stars are
termed “active galaxies”
First recognized active galactic nuclei (AGN) were Seyfert Galaxies (Carl Seyfert, 1940s)
Extremely bright, point-like nuclei
Strong and broad emission lines -- non-stellar
Highly ionized species
Types of AGN: Seyfert and Markarian galaxies, radio galaxies, quasars, LINERS, Bl Lac objects, OVVs, blazars, broad-line radio galaxies...
Feels a bit like stamp collecting -- but, their exists a single “Unified Model” for what makes an AGN.

24. Unification Scheme for Active Galaxies
Energy is derived from accretion onto super massive black holes
There is an accretion disk, likely fed by a circumnuclear torus, or the tidal disruption of stars in a nuclear cluster
The jets often seen emanating from the nuclei of active galaxies are confined by a pc scale molecular torus
Broad lines come from gas (up to 1000 M) photoionized by very hot accretion disk within 1 pc of the super-massive black hole
Narrow lines come from gas (up to 109 M) in regions 10 to 1000 pc from the nucleus.

25. AGNs: Unified Model outflowing jets
dusty molecular torus
infalling stellar and gaseous material
narrow line region
outflowing jets
broad line region
accretion disk
AGNs: Unified Model

26. Tests of the Unified Models
The Model: Difference between Seyfert 1 and Seyfert 2 galaxies is a geometric selection effect
Seyfert 1 are viewed face-on so that the broad line region is visible
Seyfert 2 are viewed edge-on so that the broad line region is obscured by the torus.
Artist’s conception of the doughnut shaped torus that confines the emission from an active nucleus (Credit ESA).

27. Detecting the Confining Torus
The confining torus should be both very warm (1000 K), and very dense (~ 107 cm-3): easily detected in the far-IR dust and line emission (CO, [OI], H2O; Krolik & Lepp,1989)
For example, the CO rotational line emission is predicted to peak near J ~ 58, or 48 m:
L58-57 ~ 7  1040 fabsLX44 ergs-s-1 & L17-16 ~ 2  1039 fabsLX44 ergs-s-1*
Typical source at 100 Mpc has a line flux of ~ 6  W-m-2
High J CO lines are clear signatures of the confining torus – and are very sensitive to the physical conditions of the torus
The high J CO lines are the primary coolant for the torus – for a warm, optically thick cloud, the luminosity is proportional to J3.
Why hasn’t this been detected?
Predictions are significantly below the detection limits of ISO/LWS at 48 m and 153 m – however, CCAT could detect such a source in the CO(13-12) line at 200 um with SNR ~ 100 in 20 minutes
*fabs is the fraction of hard x-ray emission absorbed by the torus (~10%), and LX44 is the ionizing luminosity in units of 1044 ergs –s-1 (Krolik & Lepp,1989)

28. Why use CCAT?
Low and mid-J line emission may be difficult to detect due to intervening molecular ISM heated by starburst
A key to detection is spatial resolution: to pull the CO emission out of the foreground gas, and the wavelength coverage needed address CO lines only excited in the torus
CCAT has advantages over other platforms
CCAT’s spatial resolution is as better than contemporaneous platforms (e.g. SOFIA or Hershel) in the far-IR
The far-IR CO lines are by far the most sensitive to the physical conditions of the torus, so that CCAT adds unique and important information even if ALMA can spatially resolve the source in the submillimeter CO lines

29. CCAT beam at 200 m
Line flux prediction ~ 5  105 L , or 7  W/m2! – easily detectable SNR 100 in 20 minutes.

30. CCAT and Nearby Galaxies
Spatial resolution:
2.5” – 30” from 40 – 500 m
 Mpc (NGC 253)
 Mpc (M83)
 240 – Mpc (NGC 1068)
Can, or nearly can:
Resolve individual GMCs in nearby galaxies
Resolve arm/interarm/bar interfaces in nearby galaxies
Distinguish the accretion disk from the torus for very close galaxies, e.g. the Galactic Center
Distinguish the torus compared with parent galaxy for nearby active galaxies
Sensitivity:
10,000 times greater than prior platforms, and 100 times more sensitive than Herschel
Sufficient to map half a dozen nearby galaxies in several lines in a few hundred hours
Sufficient to undertake a survey of nearby AGN for high J torus emission