1 / 12

Evolution of the IGM/Galaxy Halo Interface to z=2

Evolution of the IGM/Galaxy Halo Interface to z=2. Chris Churchill (New Mexico State University) Wal Sargent (Caltech) Michael Rauch (Carnegie). Evolution of the IGM/Galaxy Interface to z=2. Abstract.

brita
Download Presentation

Evolution of the IGM/Galaxy Halo Interface to z=2

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. Evolution of the IGM/Galaxy Halo Interface to z=2 Chris Churchill (New Mexico State University) Wal Sargent (Caltech) Michael Rauch (Carnegie)

  2. Evolution of the IGM/Galaxy Interface to z=2

  3. Abstract Weak MgII absorbers, defined to have W(2796)<0.3 Ang, are sub-Lyman limit (optically thin in HI) gaseous structures with moderately high hydrogen densities (~0.1 cm-3 ). Their direct connection with galaxies is only now being understood; it is becoming clear that weak MgII absorbers probe gas enriched by stars in the highly extended regions of galaxies and/or the Lya forest associated with galaxy mass overdensities. As such, the region probed by weak MgII absorption is in the regime of the IGM/Halo interface of galaxies. Currently, weak MgII absorption has been surveyed only over the redshifts of 0.4<z<1.4 (Figure 1, the red data) to a sensitivity of 0.02 Ang, whereas stronger MgII absorbers have been surveyed over 0.3<z<2.2 (blue data). We have extended the survey of weak MgII absorbers to match that of the strong absorbers, using 78 HIRES/Keck spectra of high redshift QSOs. FIGURE 1. --- The redshift coverage of Mg II absorbers is shown for each of two survey detection threshold sensitivities, 0.3 (blue) and 0.02 Ang (red). Weak systems have not previously benn explored for z>1.4

  4. Weak Systems at 0.4<z<1.4 Churchill etal. (1999) surveyed weak MgII using 26 HIRES/Keck QSO spectra. They found that the number density of weak systems is a factor of few more than the strong systems and that the systems apparently do not evolve in number and/or gas cross section. In Figure 2 (left) panel), the solid curves provide the no-evolution expectations. For these redshift ranges, both weak and strong MgII absorbers are consistent with a constant co-moving redshift path density. Churchill etal, (1999) Steidel & Sargent (1992) FIGURE 2. --- (left) The redshift path number density for weak MgII (red) and strong MgII (blue). --- (center) The equivalent width distribution of MgII absorbers is a power law with power -1. --- (right) Examples of HIRE/Keck weak MgII data shown in the rest-frame wavelength in order of increasing redshift from top to bottom.

  5. Relationships to Galaxies I. Q0002+051 (Example of z<1 MgII Absorbers) In the case of the z=0.59 system (lower left), there is association with a galaxy; W=0.10 A. In the case of the very weak systems (upper left, lower right), W<0.05 A, there are no obvious associated galaxy candidates… Statistically, if weak systems arise in halos of normal bright galaxies, then the sizes extend to ~70 kpc. We are currently undertaking a study to examine the extent of gas at these large projected galactocentric distances Strong System Very Weak System Very Weak System Weak System FIGURE 3. --- WFPC-2/HST Image with background QSO. Four intervening MgII absorbers are on this sightline. There are no galaxies ID’d for the two weakest absorbers. [Churchill etal (1999); Churchill & Vogt (2001); Kacprzak etal (2004)]

  6. Relationships to Galaxies II. Weak MgII Absorbers Churchill (2001) FIGURE 4. ---The host galaxies of MgII absorbers shown in order of increasing QSO-galaxy impact parameter. Three are “weak” absorbers with W>0.1 A, which are among the larger W weak systems. These three have relatively large impact parameters ranging from 23-36 kpc. Are these probing the IGM/halo region? We are currently building a sample of galaxies associated with weak systems.

  7. Relationships to Galaxies III. Steidel etal (2001) [also see the Tuesday talk by G. Kacprzak (NMSU)] compared the kinematics of the galaxies and the Mg II absorption in five edge on galaxies. One was a weak system. For the strong systems, the absorption kinematics was clearly coupled to the galaxy rotation kinematics… In the case of the weak system (right) the gas kinematics is not coupled to the galaxy rotation, which is toward the observer nearest the QSO sightline (the “+” is the direction of increasing arc seconds along the slit). By all standards, this galaxy should give rise to strong MgII absorption (Steidel 1995). Is this weak absorption IGM/halo interface material, which is apparently decoupled from the galaxy disk? (Steidel et al. 2002) X FIGURE 5. --- (top) HST image of the QSO/galaxy. The orientation of the slit for the galaxy spectrum is shown. (bottom) the galaxy kinematics and the MgII kinematics with v=0 km/s being systemic of the galaxy.

  8. High Redshift Survey Results, Redshift Range 1.4<z<2.3 • 72 HIRES/Keck spectra • Search continuum redward of Lya emission line • 85% complete for Wmin=0.02 A • Total Integrated Redshift Path Z = 11.5 • Found 10 systems Table I. High Redshift Weak MgII Systems SL is the significance level of the MgII 2796 transition. FIGURE 6. --- W(2796) vs. Absorption Redshift. Blue data are z<1.4 from Churchill etal (1999). Red data are z>1.4 from this work; the data are listed in Table I.

  9. High Redshift Survey Results, The Data FIGURE 7. --- Eight of the ten z>1.4 HIRES/Keck MgII 2796,2803 doublets plotted in rest-frame wavelength. The absorption redshift increases from upper left to lower right. Some of these system lie in the continuum, blueward of the CIV emission line of the QSO, so there are intervening CIV systems that can confuse the spectra. Also, many atmospheric features make the accounting of the redshift path length a challenge.

  10. RESULTS: Evidence for Evolution At z>1.4, the data are suggestive of a drop in the redshift number density, in that it falls below no-evolution expectations. We have plotted the no-evolution curve (red) for the currently accepted cosmological model, the blue curve is for a Friedmann universe. Computing the redshift number density is sensitive to the measured redshift path of the survey. We have carefully corrected for path length loss by atmospheric lines and by the presence of other metal systems. Evolution expected for optically thin gas over this precise redshift range? FIGURE 8. --- The redshift path number density of weak MgII absorbers over the full redshift range of 0.4<z<2.3. The red and blue curves provide the no-evolution expectations for two cosmologies. The shaded region is the new survey (this work) and is the region where evolution appears to set in.

  11. Evolution Explained The evolution in weak MgII occurs over the redshift range where the number density of QSOs is peaking a full two orders of magnitude above z=0.8 values. The QSOs are a major source of HI ionizing photons at the Lyman edge. It would seem natural that MgII in optically thin HI clouds (like the forest) would be ionized into MgIII and higher. In fact, the evolution in HI as seen in the break at z=1.7 of the Lya forest redshift number density (due to combine ionization and structure growth evolution, Dave’ etal 1999) is consistent with this suggested scenario. l912 Space Density Lya z-path Density QSO Space Density FIGURE 9. --- (left) QSO space density as function of redshift. --- (center) Space density of hydrogen ionizing photons (solid curve) as a function of redshift. --- (right) Redshift path density of low column Lya forest clouds as a function of redshift. The shaded regions are the redshift range from 1.4<z<2.2, the region where weak MgII evolution occurs. Note the turnover in all three distributions in this redshift range.

  12. Conclusions We have measured evolution in the population of weak MgII systems. The number per unit redshift increases dramatically from z=2.3 to z=1.4, where as the number is consistent with no evolution for z<1.4. This break in the redshift density coincides with the significant reduction in the number density of QSOs and HI ionizing photons, and the evolution in the Lya forest over this same redshift range. This evolution suggests that the IGM/halo interface is more highly ionized at z=2 than at z=1, assuming the HI column densities of higher redshift weak MgII systems do not evolve from z=1. At higher redshift, z=3, stellar photoionization may again cause another break in the evolution of the IGM/Halo interface ionization balance (due to softer radiation fields). We now have 51 UVES/VLT data that we are studying. We plan to complete this work by surveying a total of 150 HIRES/Keck+UVES/VLT data to significantly reduce the error bars over the full redshift range 0.4<z<2.3. References Churchill, C.W., Rigby, J., Charlton, J.C., & Vogt, S.S. 1999, ApJS, 120, 51 Churchill, C.W. 2003, in “The IGM/Galaxy Connection,” ed. J. Rosenberg & M. Putman, p149 Dave’, R., Hernquist, L., Katz, N., & Weinberg, D. 1999, ApJ, 511, 521 Scott, J., Bechtold, J. Morita, M., Dobrzychi, A., & Kulkarni, V.P. 2002, ApJ, 571, 655 Steidel, C.C., 1995, in “QSO Absorption Lines,” ed. G. Meylan, p139 Steidel, C.C., Kollmeier, J.A., Shapley, A., Churchill, C.W., Dickinson, M., & Pettini, M. 2002, ApJ, 570, 526 Steidel, C.C., & Sargent, W.L.W. 1992, ApJS, 80, 1 Weymann, R.J., Jannuzi, B.T., Lu, L. 1998, ApJ, 506, 1

More Related