Opacity of Spiral Galaxy Disks Extinction measurements from
- Slides: 31
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 – 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 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 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 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. 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. • 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 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 • 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. • 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 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. (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 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. • 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 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. (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 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 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 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 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 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? • 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 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 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 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 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 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 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 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 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 Scale Key Project • Drizzled, analyzed & combined. Holwerda et al. (2005 a, b) 4 June 2005 Island Universes Benne W. Holwerda
- Elliptical, spiral and irregular.
- Emblem
- Spiral galaxy
- Spiral galaxy
- Spiral circle spiral
- Structure architecture definition
- Modal opacity
- Greensock parallax
- Atmospheric opacity
- Flat iris insertion in congenital glaucoma
- Opacity and translucency in insulators
- Bio.alphabet has been removed from biopython
- Line opacity
- Digital smoke ogden ut
- Atmospheric opacity
- Probability learning objectives
- Tower of hanoi 4 disks
- Holger brock
- Magnetic disks are the most popular medium for
- Aka.ms.sqlcapacity
- Raid redundant array of inexpensive disks
- Conquest data disks
- Fixed-head magnetic disk storage
- Disks and tapes can be stored ------- a library. eng101
- Parts of
- Redundant arrays of independent disks
- Raid 5 nedir
- Floppy disk
- Milky way galaxy sketch
- Galaxy classification
- C5 galaxy cockpit
- Ngc 2147 galaxy classification