Updated: 6 March 2011

Collaborators: Genevieve Graves, Jason X. Prochaska (UCSC)

Conference presentation (pdf) from The Cosmic Odyssey of the Elements, Aegina, Greece, June 2008

1. Revealing the Enrichment of the IGM

   Thank you for the time to share our preliminary results on a specific aspect of IGM enrichment---namely the galaxy-IGM (or halo)--- connection. Since it's evening, mid-week, I'll engage your interest by revealing my results first.

2. Galaxy-IGM Metals Connection?---TEASER

   Plotted here is the C-on-N abundance relative to solar of the galaxies over the IGM cloud that's likely in the halo (owing to small impact parameter and small velocity offset). What you can see is that for this IGM cloud, which is close to two similar galaxies, the [C/N] abundance is comparable to the galaxy. The same is not true for this other galaxy and field. This is the type of plot we plan to flesh out in the future.

3. Odyssey of Elements

   Here's my generic cartoon of the odyssey of the elements. It's biased by my IGM-ist point of view. I want to focus us on the IGM-halo-galaxy boundary of the whole IGM enrichment scheme. We're asking the specific question: what is the relationship between the metals in the galaxy and the metals in the nearby IGM (halo).

4. Galaxy-IGM Connection

   It is known that there is a galaxy-IGM connection. Here is the "bull's-eye" view of galaxies IGM folk keep in their heads. HI column density increases with decreasing impact parameter (denoted ρ---not density). And within ~100 kpc of a galaxy there often metals. This is shown empirically on the right where impact parameter in Mpc is plotted over HI column density for two LOS (red and blue). The crosses are Lyα-only absorbers, and the pluses are metal-line systems. You can see that they tend to be associated with HI column density > 10¹⁵ cm^-2.

5. Pilot Study: Tools at Hand

   The tools we're suing for this pilot study into "what is the relationship between the metals in the galaxy and the metals in the nearby IGM (halo)?" We start with galaxy surveys around low-redshift (z < 0.5) quasars. As shown on the right, the blue is all glaaxies in the survey with |δv| < 500 km/s of a published LLS. The field is 20' by 20' which is ~2 Mpc at z = 0.1 and is 100% complete within 5' (500 kpc) to R = 20 mag (0.07 L_*). For the fields of our surveys, we find published logN_HI > 15 absorbers and see if they have a close galaxy in our survey. We define close to be ρ < 150 kpc and |δv| < 500 km/s. Then we get higher S/N spectra of those galaxies and measure metallicities.

6. Metals in IGM

   Here are examples of the metals we can measure in the high-column density IGM. These are velocity plots. For those not familiar with them, you basically stack each line associated with a given redshift so that the expected observed wavelength is consistent with v = 0 at the redshift of the absorber. It's a good way to see consistency in profile shape and alignment. Common metals are Si, C, O, N, Fe.

7. IGM Metallicities: CLOUDY

   IGM metallicities are based on measured column densities of the elements and the ionization corrections from CLOUDY. Plotted here is the model ionic ratio between two ionization of the same species over the ionization parameter, which is the number of 1 Ryd photons per H atom. The model is for 10^16.25 cm^-2 HI column density and Z = 1/3 Z_SUN (scaled). The measured column densities constrain logU, which we use to get the ionization correction. We want to note that these values are our re-analysis of Sembach's work (updated CLOUDY models, new metal column densities).

8. Metals in Galaxies

   Here are the galaxy spectra. You can see the type and statistics of each galaxy. We use Lick indices to measure metallicity but all those aren't marked. For instance, the C₂ band is ~4668 Å. Dichroic cutoff MgII.

9. Galaxy Metallicities: EZ_Ages

   EZ_Ages by Jenny and Ricardo is publically available (so check it out). The abundance of each element Mg, C, N, Fe, Ca is iteratively toggled until the solution is consistent. Consistent can be thought of as the model spectrum matching or as is truly the case, sliding grids around.

10. Galaxy Metallicities

    Here are the metallicity results for the galaxies. Two striking results: (1) FJ2155 galaxies are old, metal-poor (caveat: unsure) and (2) they are C-enhanced relative to N (or N-deficient). [C/N] above and beyond what is seen in the field. As shown in this plot of [C/N] versus velocity dispersion. (By the way, I personally thank Arjen van der Wel for helping me measure dispersions). The black points are SDSS early-type galaxies from Graves et al (2007). The two fields (and galaxies) are shown as well as the constraints on the IGM (shading).

11. Future Work

    Before I show my results plot again, I want to touch on our future work. It's the usual fair: more data. I want to emphasize this unexplored avenue of investigation: why are early-type galaxies as often the closest galaxies. Chen et al (2005) found that the 10¹⁴ cm^-2 HI-galaxy two-point correlation goes away when the galaxies are only early types.

12. Galaxy-IGM Metals Connection?

    Now you should better understand the origin of this plot. It's full implications are yet to be determined. Questions?