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CCAT Studies of Nearby

Galaxies

Gordon Stacey

Cornell University

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CCAT: The Nearby Universe

Starforming galaxies Continuum studies Spectral line studies Examples

Active galactic nuclei: revealing the torus

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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 extincted by many magnitudes of dust, e.g. the Galactic Center suffers 28 magnitudes!

Cooling power – clouds must cool to collapse and form stars The light from young stars is absorbed locally by dust,

and reradiated in the far-IR and submm 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

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Motivation Cooling power – clouds must cool to collapse and

form starsThe 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?

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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.

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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.

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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

Visible

IRAS ISO 175 m

M31: Haas et al. 1998

Continuum Observations

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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)

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NGC 891 Imaged at 450 and 850 um with

SCUBA on JCMT (Alton et al. (1998, Israel et al. 1998)

Traces cold (T~ 17 K) dust in the disk

There appears to be emission at large scale heights in both images, but this is likely the exponential tail of the galactic plane

At the resolution of the JCMT images, less than 5% of the dust lies out of the main extinction lane

At the higher resolution and sensitivity possible with CCAT, it is likely we will that superbubbles and chimneys will appear tracing the expulsion of dust from the disk.

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Far-IR Continuum: Revealing the Starburst

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!

Charmandaris, Stacey and Gull 2002)

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NOAO: M. Rushing

The Antennae Galaxy

Spitzer IRAC ImageSubmm: SHARC-2

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Time to Image Galaxies The Antenna can be imaged very rapidly

In the 350 um continuum, the extended emission has a flux density of 0.2 Jy per 10” beam, or 20 mJy per 3.5” beam

In 200 seconds, CCAT attains a flux limit of 1 mJy/beam, or SNR ~ 20

The flux is ~10 times smaller (per beam) at 850 um, but the beam is 850 ~ 6 350 and, with > twice the sensitivity at 850 um, we obtain SNR ~ 30 in 200 seconds

Even at 200 um: SNR ~ 10 in 1.6 hours of integration time. Image the Antennae in 4 bands (200, 350, 450, 850 um) in less

than 2 hours, or only 10 minutes without the 200 um band! For the less intense M83 system, a typical flux per beam is ~ 4

mJy @ 350 um, so that it takes ~ 1.3 hours to reach SNR > 20 over the 5’ FOV of the short submm camera.

Image M83 in 43 bands (350, 450, 850 um) in 4 hours.

Would survey the brightest 100 nearby galaxies including quiescent spirals and starbursters

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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 ionized gas density. [NII] 3P1-3P0 (205 m) line has

same density dependence as [CII] for ionized gas constrains fraction of [CII] from ionized gas

For density bounded HII regions, the [NII] lines probe the ionizing photon rates: NLyman continuum Wright et al. 1991

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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 609 and 370 m [CI] lines are

ubiquitous Line ratio is near unity,

temperature sensitive Tgas ~ 40 K

The combined cooling in the 370 and 610 m 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

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Unique Spectral Lines Available to CCAT

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

Species Transition E.P.1 (m) A (s-1) ncrit (cm-3)2

N+ 3P1 3P0 70 205.178 2.1 10-4 4.8 101

C0 3P2 3P1

3P1 3P0

63

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370.415

609.135

2.7 10-7

7.9 10-8

1.2 103

4.7 102

12CO  13CO

J = 1312J = 1110J = 7 6J = 6 5J = 6 5

503430155116111

200.273236.614 371.651433.338453.497

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-.

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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 massIt 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

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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(76) 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

-0.5

0

0.5

1

1.5

2

2.5

3

1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06

Density

CO

(7-6

)/[C

I] L

ine

Rat

io

G = 10

G = 100

G = 1000

G = 10000

G = 100000

CO(7-6)/[CI] 370 m line intensity ratio vs. density for various values for the strength of the ISRF, G (Kaufman et al. 1999)

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Submm Line Observations: The [CI] and mid-J CO Lines

The CO(65) line first reported from a few starburst nuclei (Harris et al. 1991) Gas is both warm, and dense – modeling was fit into a PDR

(stellar UV heating) scenario Several galaxies detected & mapped in the [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 starburst

galaxies – much higher than Milky Way values. This is due to: Fractionally more photodissociated gas due to cloud fragmentation Production of Co in molecular cloud interiors due to processes

associated with high cosmic ray fluxes or non-equilibrium chemistry

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Starburst Galaxies: Mid-J CO

SPIFI CO(76) mapping of NGC 253 shows emission region extends > 500 pc

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

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Starburst Galaxies: Mid-J CO and [CI] 370 um Lines

[CI] and CO(76) lines simultaneously mapped from NGC 253:

The [CI]/CO(76) ~ 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(76) (372 um) spectrum of the NGC 253 nucleus

[CI] CO(76)

TMB = 1 K

Added heat at cloud cores will inhibit cloud collapse – halting starburst

Nikola et al. 2005

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[CI] line is constant and ubiquitous, it cools the overall ISM

CO(7 6) is greatly enhanced at the starburst interaction zone reflecting the high gas excitation there

Strong mid-J CO emission reflects influence of OB stars

CO(7-6) and [CI] from the Antennae Galaxy

Interaction Zone

[CI] CO(7-6)

TMB = 200 mK

21” region

[CI] CO(7-6)

TMB = 100 mK

30” region

[CI] CO(7-6)

TMB = 50 mK

Isaak et al. 2005

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Bars, Spiral Arms, and Starformation: M83

ISO mapping shows how the far-IR lines trace starformation with 70” beam

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 ~ 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

ISO: [NII] 122 m ISO: [CII] 158 mISO: [OIII] 88 m

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Bars, Spiral Arms, and Starformation: M83

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?

ISO: [OIII] 88 m

3” [CI] beam 70 pc

6” Resolution CO (1-0) Map on false-color HI (Rand Lord, & Higdon 1999)KAO Map in [CII] 55” Beam (Geis et al.)

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[NII] is Detectable from the Ground

We mapped the [NII] distribution from Carina nebula using SPIFI at the South Pole in 2.9% zenith transmission!

Good days at South Pole or for CCAT might expect ~ 20% transmission

-0.1

0

0.1

0.2

0.3

0.4

0.5

-201 -139 -78 -16 45 107 168

Flux

Fit

vLSR

TMB

Position of Carina 2345678

Oberst et al. 2005

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Time to Map M83Suppose we map M83 in the [CI] 370 m line:

Beam size ~ 3.7”, or 90 pc at 5 MpcMap eastern spiral arm: 2’ 3’ regionRequires 800 pointings for sparse (single beam) sampled mapPredicted line flux is ~ 1 10-17 W-m2 in 3.7” beam 16 seconds of integration time yields SNR ~ 20Total time for project: 7 hours including a factor of 2 for overheads with a single pixel receiver!Entire galaxy (35 square arcmin) takes 40 hoursA 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 hourWith modest array format along dispersion direction (12 to 16 pixels) would have a map in CO(76) as well.

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Edge on Galaxies: NGC 891

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 ~ 200-300 pc (4 to 6”) so that

the galactic plane will be resolved.

2” beam 100 pc

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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 botany -- but, their exists a single “Unified Model” for what makes an AGN.

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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.

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AGNs: Unified Model

dusty molecular torus

infalling stellar and gaseous material

narrow line region

outflowing jets

broad line region

accretion disk

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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).

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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 10-18 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(1312) 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)

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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

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CCAT beam at 200 m

Line flux prediction ~ 5 105 L , or 7

10-17 W/m2! – easily detectable SNR 100 in 20 minutes.

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CCAT and Nearby Galaxies Spatial resolution:

2.0” – 8.5” from 200 – 850 m 24 -- 100 pc @ 2.5 Mpc (NGC 253) 50 -- 200 pc @ 5 Mpc (M83) 200 – 800 pc @ 20 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 to 40 times greater than prior platforms, and comparable to ALMA per beam for point sources especially in the continuum

Sufficient to map a hundred nearby galaxies in the continuum and several lines in a few hundred hours

Sufficient to undertake a survey of nearby AGN for high J torus emission

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SPARE SLIDES

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Redshifted [CII] The [CII]/far-IR continuum is a

sensitive indicator of the strength of the ambient ISRF, G The [CII] line detection yields the concentration of the starburst In regions with the highest UV

fields (young starbursts, AGNs), the [CII]/far-IR continuum ratio is depressed

Reduced efficiency of photoelectric effect

Increased cooling in [OI] 63 m line

More diffuse fields (like M82) results in larger [CII]/far-IR ratio

Detecting [CII] from highly redshifted galaxies probes star formation in the epoch of galaxy

formation

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+01 1.E+03 1.E+05

DensityR

= [C

II]/F

IR

G = 10

G = 100

G = 1000

G = 10000

The [CII]/far-IR continuum ratio as a function of G (from Kaufmann et al)

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The Redshift (z) and Early Universe Spectrometer (ZEUS)

A device as simple as an echelle grating spectrometer can detect this line as the orders of the echelle match the telluric windows

Spectral coverage of ZEUS, superposed on the Mauna Kea windows.

ZEUS Spectral Coverage

Dual stage 3He refrigerator

4He cryostat

M5: Primary

Grating

Detector Array

Scatter Filter

LP Filter 1

LP Filter 2

BP Filter Wheel

M1

M2

M3

M4

M6

4He Cold Finger

Entrance Beam

f/12

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Far-IR Lines and the Early Universe One can detect the [CII] line and several other

far-IR lines in the redshift intervals from 1 to > 5 [CII] PDRs, low density HII regions, atomic

clouds [OI] PDRs [NII] low density HII regions [OIII] HII regions, O stars

Covers just the region of redshift space where the most evolution per co-moving volume occurs, and also where the UV/optical techniques are most affected by extinction

ZEUS Windows

Estimates of the comoving star formation history (Blain et al). Filled squares and circles toward the bottom represent the original Madau plot based on optical/UV HDF observations (Madau et al). Open squares correct this data for dust extinction (Pettini et al). The 7 upper curves are models that are consistent with the SCUBA data. The solid lines beneath the curves mark the redshft ranges accessible to ZEUS.

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Line Redshift Interval

Window Lfar-IR [L] Fline[W m-2]

[CII]: 157.741 m

1.10 1.39 1.69 2.02 2.74 2.97

3.7 4.5 6.0

350 m

450 m

620 m 740 m 865 m

1103 m

> 8 1010

> 1.3 1011

> 3.1 1011

> 2.1 1011

> 3.0 1011

> 2.7 1011

1.1 10-19

7.7 10-20

6.6 10-20

2.3 10-20

1.6 10-20

8.4 10-21

[NII]: 121.898 m

1.72 2.12 2.48 2.91 3.84 4.14

350 m

450 m 620 m

> 1.1 1012

> 2.1 1012

> 3.6 1012

1.1 10-19 7.7 10-20

6.6 10-20

[NII]: 205.178 m

0.70 0.84 1.07 1.33 1.88 2.06

350 m

450 m 620 m

> 1.7 1011

> 5.6 1011

> 1.1 1012

1.1 10-19 7.7 10-20

6.6 10-20

[OIII]: 88.356 m

2.75 3.27 3.80 4.40

350 m

450 m > 1.0 1012

> 1.9 1012 1.1 10-19 7.7 10-20

[OI]: 63.184 m

4.24 4.97 5.71 6.55

350 m

450 m > 4 1012

> 5 1012 1.0 10-19

7.7 10-20

Far-IR Lines from High-Z Galaxies Detectable with CCAT

The calculated sensitivities are 5 in 10,000 secs on CCAT Our continuum surveys will uncover many tens of

thousands of distant galaxies observable in their [CII] line radiation with direct detection spectrometers

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Redshifted [CII] Emission Yields Far-UV Field Strength and Redshifts

The [CII] line is detectable at redshifts in excess of 5 for Lfar-IR > 3 1011 L

ULIGS have L > 1012 L,, and [CII]/far-IR > 0.03% -- [CII] still readily detectable!

It is the lower luminosity systems that are most interesting with respect to galaxy assembly – these will likely have relatively bright [CII] line emission

[CII] line is uniquely bright, but redshifts can be verified (again with a gain to the physical understanding) by observing the other bright far-IR lines.

Milky Way

ULIGS