Opacity of Spiral Galaxy Disks Extinction measurements from

  • Slides: 31
Download presentation
Opacity of Spiral Galaxy Disks Extinction measurements from counts of distant galaxies. B. W.

Opacity of Spiral Galaxy Disks Extinction measurements from counts of distant galaxies. B. W. Holwerda (Kapteyn/ STSc. I) R. J. Allen (STSc. I) R. A. González (UNAM, Morelia) P. C. van der Kruit (Kapteyn) 4 June 2005 Island Universes Benne W. Holwerda

Finding dust in spirals • To characterize dust in spirals: – Emission: infrared/sub-mm –

Finding dust in spirals • To characterize dust in spirals: – Emission: infrared/sub-mm – Extinction: SED models, background objects. • Different strengths & weaknesses: – Emission depends on dust temperature and hence illumination and dust emissivity is still uncertain. – Extinction needs a known background source. => We use the number of distant galaxies as the background. 4 June 2005 Island Universes Benne W. Holwerda

Counting Galaxies • Calibration issues: – Crowding: are the distant galaxies hidden by stars

Counting Galaxies • Calibration issues: – Crowding: are the distant galaxies hidden by stars or dust? – Confusion: what is a foreground object and what is a distant galaxy? – Clustering: are the distant galaxies blocked by dust or simply not there? 4 June 2005 Island Universes Benne W. Holwerda

The “Synthetic Field Method” 1. Identify distant galaxies in science field. 2. Combine image

The “Synthetic Field Method” 1. Identify distant galaxies in science field. 2. Combine image with dimmed HDF-N/S. 3. Identify background galaxies in simulations. 4. Fit relation between simulated background galaxies and dimming: A = -2. 5 Log(N/N 0) 5. Estimate opacity from the intersection of fit and number from the science field. González et al. (1998) Holwerda et al. (2005 a) 4 June 2005 Island Universes Benne W. Holwerda

Beating statistics • The HDF has ~100 easily recognizable field galaxies, in a crowded

Beating statistics • The HDF has ~100 easily recognizable field galaxies, in a crowded field, ~30 remain. • Beating statistics with more data; deeper impractical, analyze more fields with automated method Holwerda et al. (2005 a). • Combine 32 HST/WFPC 2 fields based on common characteristics e. g. : – – Radius, distance from foreground galaxy center Arm, inter-arm and outside disk regions Disk surface brightness HI column density 4 June 2005 Island Universes Benne W. Holwerda

Radial extinction plots • Scale all radii with R 25 (de Vaucouleur et al.

Radial extinction plots • Scale all radii with R 25 (de Vaucouleur et al. 1991) • Find background galaxies, synthetic and real, in radial annuli. • Combine counts and derive opacity (AI) 4 June 2005 Island Universes Benne W. Holwerda et al. (2005 b)

Arm and disk regions • Divide fields into arm/inter-arm and outside disk regions. •

Arm and disk regions • Divide fields into arm/inter-arm and outside disk regions. • Compare to similar results from occulting galaxy technique • Points from White et al. (2000) and Domingue et al. (2000). 4 June 2005 Island Universes Benne W. Holwerda et al. (2005 b)

Galaxy colors: patchy dust • Average color of background galaxies independent of the inferred

Galaxy colors: patchy dust • Average color of background galaxies independent of the inferred opacity. • Grey extinction known effect of patchy dust. • Extinction measured from missing number, color from remaining galaxies. • Distant galaxies are extended objects 4 June 2005 Island Universes Benne W. Holwerda et al. (2005 b)

Dust and light • Flag each background galaxy with the 2 MASS pixel value

Dust and light • Flag each background galaxy with the 2 MASS pixel value • Sort the galaxy counts per surface brightness • SB-A relation in arms, not in the disk. 4 June 2005 Island Universes Benne W. Holwerda et al. (2005 d) submitted

Compare to SCUBA sub-mm • Radial Profiles of submm emission and opacity values match.

Compare to SCUBA sub-mm • Radial Profiles of submm emission and opacity values match. • Individual measurements of opacity are uncertain. • Little overlap in current samples. Much future work for SCUBA and ACS. Meijerink et al. 2005 4 June 2005 Island Universes Benne W. Holwerda et al. (2005 c) A&A accepted

Comparison to HI • Radial surface density profiles HI(r) from the literature. • Compare

Comparison to HI • Radial surface density profiles HI(r) from the literature. • Compare to individual opacity profiles. • No apparent relation between HI and opacity. 4 June 2005 Island Universes Benne W. Holwerda et al. (2005 c) A&A accepted

Average Dust-to-HI ratio Boissier et al. (2004) Cuillandre et al. (2001) Thomas et al.

Average Dust-to-HI ratio Boissier et al. (2004) Cuillandre et al. (2001) Thomas et al. (2005) Mayya et al. (1997) • Average opacity profile • Average HI profile • Compare ratio. • Higher than earlier estimates. • Similar to sub-mm estimates. Issa et al. (1990) 4 June 2005 Island Universes Benne W. Holwerda et al. (2005 c) A&A accepted

Conclusions (1) • SFM calibrates biases and errors in field galaxy numbers. • Spiral

Conclusions (1) • SFM calibrates biases and errors in field galaxy numbers. • Spiral disk show AI < 1 magnitude of extinctions within the R 25 • Later type spirals slightly more opaque than earlier types. • Arms are more opaque than the disk. • Dust in the disk is patchy. 4 June 2005 Island Universes Benne W. Holwerda

Conclusions (2) • Surface brightness and opacity are linked, especially in the spiral arms.

Conclusions (2) • Surface brightness and opacity are linked, especially in the spiral arms. • Dust responsible for opacity appears cold when compared to sub-mm emission. • HI column density and opacity appear not linked. • The ratio of the average opacity profile and the average HI profile poinst to more dust per HI. 4 June 2005 Island Universes Benne W. Holwerda

Future Work • ACS imaging of M 101 and M 51 • Direct comparison

Future Work • ACS imaging of M 101 and M 51 • Direct comparison to HI column density and IR/sub-mm emission. • Fully automated object classification. Image courtesy of K. D. Kuntz 4 June 2005 Island Universes Benne W. Holwerda

More Questions? • My thesis is done! • Results also in holwerda et. al.

More Questions? • My thesis is done! • Results also in holwerda et. al. (2005 a, b) (published) (2005 c, d, e)(submitted) • Or send me an email: holwerda@stsci. edu 4 June 2005 Island Universes Benne W. Holwerda

Cepheid reddening & opacity • Average reddening of the Cepheids in the fields is

Cepheid reddening & opacity • Average reddening of the Cepheids in the fields is converted to extinction. • Opacity from number of galaxies mostly similar. • Detection bias in Cepheids at higher values. 4 June 2005 Island Universes Benne W. Holwerda et al. (2005 d) A&A submitted

Limiting factors • González et al. (2001) predicted that galaxies at Virgo distances are

Limiting factors • González et al. (2001) predicted that galaxies at Virgo distances are optimum for SFM analysis. • A = -2. 5 C log(N/N 0) • Surface Brightness and granularity of the disk responsible for limitations. • My data supports this conclusion. 4 June 2005 Island Universes Benne W. Holwerda et al. (2005 e) A&A submitted

An improved HI comparison • Cuillandre et al (2001) • Compare number of galaxies

An improved HI comparison • Cuillandre et al (2001) • Compare number of galaxies per HI contour. • Optimal for single disk. 4 June 2005 Island Universes Benne W. Holwerda

Object Classification All Objects HDF 4 June 2005 • Single parameter cut not sensitive

Object Classification All Objects HDF 4 June 2005 • Single parameter cut not sensitive enough • Total chance computed from all parameters. • Some hard cuts to remove blue clusters HII regions etc. • Total score works but improvements still possible. Island Universes Benne W. Holwerda

Comparing observers • NGC 4536 re-analyzed with automated SFM • Compared to the number

Comparing observers • NGC 4536 re-analyzed with automated SFM • Compared to the number of González et al (1998). • Difference due to limiting depth. Holwerda et al. (2005 a) 4 June 2005 Island Universes Benne W. Holwerda

HDF-N/S as a reference field • The HDF-N/S fields; how ``average’’ are they? •

HDF-N/S as a reference field • The HDF-N/S fields; how ``average’’ are they? • Compare numbers of objects per magnitude range to cosmological searches. • No deviation from the mean field up to the detection limit. Holwerda et al. (2005 a) 4 June 2005 Island Universes Benne W. Holwerda

Computing the Error • Relation between number of synthetic galaxies and dimming. • Measurement

Computing the Error • Relation between number of synthetic galaxies and dimming. • Measurement error in synthetic number • Measurement and clustering error in actual number. 4 June 2005 Island Universes Benne W. Holwerda

Galactic Extinction • Galactic extinction varies for each field. • Difference with the reference

Galactic Extinction • Galactic extinction varies for each field. • Difference with the reference field (HDFN/S) important. • Nearly negligible except for NGC 6946 4 June 2005 Island Universes Benne W. Holwerda

Synthetic Dust Models • Filling factor of dust clouds observed. • Many small clouds

Synthetic Dust Models • Filling factor of dust clouds observed. • Many small clouds or a few big ones? • The effects on number of distant galaxies very different. • Focus for future work. 4 June 2005 Island Universes Benne W. Holwerda

Inclination correction • Radial opacity profiles independent of inclination. • Implies that the filling

Inclination correction • Radial opacity profiles independent of inclination. • Implies that the filling factor remains the same. • Flat distribution of dust. 4 June 2005 Island Universes Benne W. Holwerda et al. (2005 b)

Disk Opacity and Hubble type • AI < 1 until R 25 • Disks

Disk Opacity and Hubble type • AI < 1 until R 25 • Disks early types more opaque than later types? • LSB transparent. 4 June 2005 Island Universes Benne W. Holwerda et al. (2005 b)

Disk surface brightness • Relation between SB and A in radial annuli. • More

Disk surface brightness • Relation between SB and A in radial annuli. • More extinction at brighter SB. • Combine background galaxy numbers based on disk surface brightness. 4 June 2005 Island Universes Benne W. Holwerda et al. (2005 b)

Comparison to IR/sub-mm. • Cold dust best characterized in sub-mm • Very few galaxies

Comparison to IR/sub-mm. • Cold dust best characterized in sub-mm • Very few galaxies done with SCUBA • Substantial overlap with the Spitzer Infrared Nearby Galaxies (SINGS) data. • Compare radial profiles with FIR profile. 4 June 2005 Island Universes Benne W. Holwerda

Comparison to IR • SINGS overlap in sample: 8 galaxies (Feb 2005) • MIPS

Comparison to IR • SINGS overlap in sample: 8 galaxies (Feb 2005) • MIPS 160 micron maps • Compare radial profiles. • Crude but quick first look. • Dust causing opacity appears cold (T~15 -20 K) • Dust emissivity still uncertain. 4 June 2005 Island Universes Benne W. Holwerda

The Sample • 32 WFPC 2 fields in V, I • Mostly Cepheid Distance

The Sample • 32 WFPC 2 fields in V, I • Mostly Cepheid Distance Scale Key Project • Drizzled, analyzed & combined. Holwerda et al. (2005 a, b) 4 June 2005 Island Universes Benne W. Holwerda