1 / 29

Detection of the 2175 Å Dust Extinction Feature at high z

Detection of the 2175 Å Dust Extinction Feature at high z. Junfeng Wang (Penn State/UFL) Collaborators : Jian Ge (U. of Florida), Pat Hall ( Princeton U./ York U.), Jason Prochaska (UCSC/Lick Observatory),

elizabeth-garner
Download Presentation

Detection of the 2175 Å Dust Extinction Feature at high z

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Detection of the 2175Å Dust Extinction Feature at high z Junfeng Wang (Penn State/UFL) Collaborators: Jian Ge (U. of Florida), Pat Hall (Princeton U./York U.), Jason Prochaska (UCSC/Lick Observatory), Aigen Li (U. of Arizona/U. of Missouri), Don Schneider (PSU), Don York (U. of Chicago), Scott Anderson (U. of Washington) IAUC199@SHAO, Mar. 17, 2005

  2. The Broad Absorption “Bump” ”A dramatic piece of spectroscopic evidence which should have much to tell us about at least a part of the interstellar grain population.”—Draine (1989) • The 2175Å dust extinction feature was first discovered by Aerobee rocket observations (Stecher 1965) • It is seen in extinction curves along lines of sight in the Milky Way (MW), the Large Magellanic Cloud (LMC), and even some regions of the Small Magellanic Cloud (SMC). • Extinction curves in the SMC bar region lack the 2175Å feature.

  3. Empirical Extinction Curves Pei (1992) and references within

  4. Analytical Extinction Curves • CCM Galactic extinction law from Cardelli, Clayton, & Mathis (1989) Rv=A(V)/E(B-V); x=λ-1 Fitzpatrick (1999)

  5. The Broad Absorption “Bump” ”A dramatic piece of spectroscopic evidence which should have much to tell us about at least a part of the interstellar grain population.”—Draine (1989) • The 2175Å dust extinction feature was first discovered by Aerobee rocket observations (Stecher 1965) • It is seen in extinction curves along lines of sight in the Milky Way (MW), the Large Magellanic Cloud (LMC), and even some regions of the Small Magellanic Cloud (SMC). • Extinction curves in the SMC bar region lack the 2175Å feature. • The central wavelength of the feature varies by only ±0.46%~(2) around 2175Å, while its FWHM varies by ±12%~(2) around 469Å. (Fitzpatrick & Massa 1986) • Although the exact carrier is unknown, “some form of graphitic carbon is responsible”, most likely polycyclic aromatic hydrocarbons (PAHs; Joblin, Leger, & Martin 1992; Duley & Seahra 1998; Weingartner & Draine 2001; Li & Draine 2001; Draine 2003).

  6. Malhotra (1997) Previous Detections… • Malhotra (1997) reports a statistical detection in a sample of 92 QSOs at redshift 0.2<z<2.2 • Cohen et al. (1999) detected the 2175Å feature in a DLA at redshift z=0.524 toward the BL Lac object AO 0235+164 at z=0.94 -- the only previous detection from an individual intervening absorption system • Falco et al. (1999) determined extinction laws in galaxies z  1.01, with Rv estimates from 1.5 to 7.2, using gravitational lensing of background quasars.

  7. Previous Detections • Munoz et al. (2004) reported that the dust in the z=0.68 lens galaxy of B 0218+357 shows very flat UV extinction curve (Rv=12±2) • Motta et al. (2002) detected a strong 2175Å bump in a lensing galaxy at z=0.83

  8. Munoz et al. (2004) ~

  9. Motta et al. (2002) Previous Detections

  10. SDSS DR1 and DR2 • Large and well-selected samples extending to high redshifts are needed to characterize the diversity and evolution of dust properties in the early universe – SDSS quasar spectra -- See Khare et al. poster • The DR2 spectra distributed by the SDSS have been sky subtracted, corrected for telluric absorption but not for galactic extinction. • Visual inspection of the SDSS spectra of ~22000 DR2 (include DR1) quasars with z ≥ 0.9 uncovered several quasars with possible 2175Å signature. -- 3 candidates from DR1 and 12 candidates from DR2

  11. A Cartoon Illustration Quasar absorption line technique is also a powerful tool for studying dust properties at high z

  12. Vanden Berk et al. (2001) Fitting and Results • Templates: -Composite spectrum from Vanden Berk et al. (2001)

  13. Richards et al. (2003) Fitting and Results • Templates: -Composite spectrum from Vanden Berk et al. (2001) -Reddest-quartile and bluest-quartile composites from Richards et al. (2003)

  14. Comparison of Spectral Indices fλ λ-(α+2) Wang et al. (2004), ApJ, 609, 589

  15. DR2 sample showing possible bump features Mode g-i from Hopkins et al.(2004)

  16. Fitting and Results • Templates: -Composite spectrum from Vanden Berk et al. (2001) -Reddest-quartile and bluest-quartile composites from Richards et al. (2003) • Extinction curves: -Empirical extinction curves for the MW, LMC and SMC from Pei (1992)free par.: E(B-V) -CCM Galactic extinction law from Cardelli, Clayton, & Mathis (1989)free par.: E(B-V), Rv

  17. SDSS J1459+0024

  18. Reddened spectra with LMC or SMC curves can not produce sufficiently deep bump to match the observed spectrum. • The best fit is obtained with the reddest composite using CCM extinction law. • Rv=1.9(+0.3, -0.2) • E(B-V)=0.13±0.01 • Detected by 2MASS, and its J-K color of 1.22 places it in the reddest quartile of z=3 quasars (Barkhouse & Hall 2001).

  19. SDSS J0121+0027

  20. Diversity of Grain Sizes? • Surprisingly small Rv values for SDSS J1459+0024 (Rv=1.9) and SDSS J1446+0351 (Rv=0.7) • Most extreme extinction curve with Rv=2.1 in MW: line of sight towards HD 210121 high latitude translucent cloud • Previously reported minimum Rv=1.5 is associated with a lensing galaxy at z=0.96 (Falco et al. 1999) • Preferential removal of small dust grains will result in a gray extinction law with large Rv, while in star forming galaxies finer grains dominate the dust size distribution.

  21. [Fe/Zn] is very large for SDSS J0121+0027, similar to heavily depleted diffuse clouds in MW, e.g.  Oph (Savage & Sembach 1996) • Very likely DLAs indicated by the strong MgII and FeII lines (Rao & Turnshek 2000) • Among the largest in all the high-redshift DLAs searched for dust and molecular hydrogen to date (e.g., Ge et al. 2001; Ledoux et al. 2003)

  22. The 2175 Å selected dusty intervening systems are all strong MgII absorbers Wang et al. (2005), submitted to ApJ

  23. DR1 sample DR2 sample Random MgII systems

  24. Keck ESI spectra (∆v ~ 33km/s) J0121+0027 J1459+0024

  25. Voigt Profile fitting (MgII λλ2796,2803) Relative Intensity Wavelength (Å) VPFIT 6.0, R. Carswell et al.

  26. Dust Depletion Pattern Savage and Sembach (1996) Wang, Prochaska, & Ge et al. (2005), in preparation

  27. J1459 J0121 Ledoux, Petitjean and Srianand (2003), also see their poster in the next room

  28. Summary • Several spectroscopic detections of the 2175Å dust extinction feature in quasar absorption systems at redshifts z ~ 1.4 • The first detection of this feature in individual MgII absorption system. • Dust depletion for SDSS J1459, J0121 is very large, similar to heavily depleted diffuse clouds in MW • Various Rv values indicates a wide range of dominant grain sizes among intervening absorption systems. • The sample showing the 2175Å feature are all strong MgII systems with strong FeII lines (likely DLAs) and heavily reddened. • It implies that DLAs with heavy dust content should be rare (but, any evolution with z?) • It may be evidence of complex organic molecules in the young universe, if the presently favored PAH model is correct.

More Related