The Stellar UV Background at z<1.5 and the Baryon Density of Photoionized Gas

We use new studies of the cosmic evolution of star-forming galaxies to estimate the production rate of ionizing photons from hot, massive stars at low and intermediate redshifts. The luminosity function of blue galaxies in the Canada-France Redshift Survey shows appreciable evolution in the redshift interval z=0-1.3, and generates a background intensity at 1 ryd of J_L~ 1.3 x 10^{-21} f_{esc} ergs cm^{-2} s^{-1} Hz^{-1} sr^{-1} at z~0.5, where f_esc is the unknown fraction of stellar Lyman-continuum photons which can escape into the intergalactic space, and we have assumed that the absorption is picket fence-type. We argue that recent upper limits on the H-alpha surface brightness of nearby intergalactic clouds constrain this fraction to be <~ 20%. The background ionizing flux from galaxies can exceed the QSO contribution at z~ 0.5 if f_{esc}>~ 6%. We show that, in the general framework of a diffuse background dominated by QSOs and/or star-forming galaxies, the cosmological baryon density associated with photoionized, optically thin gas decreases rapidly with cosmic time. The results of a recent Hubble Space Telescope survey of OVI absorption lines in QSO spectra suggest that most of this evolution may be due to the bulk heating and collisional ionization of the intergalactic medium by supernova events in young galaxy halos.Comment: 6 pages, Latex file, 2 figures, mn.sty, MNRAS in pres

Clustering at high redshift

The addition of deep near infrared images to the database provided by the HDF-S WFPC2 is essential to monitor the SEDs of the objects on a wide baseline and address a number of key issues including the total stellar content of baryonic mass, the effects of dust extinction, the dependence of morphology on the rest frame wavelength, the photometric redshifts, the detection and nature of extremely red objects (EROs). For these reasons deep near infrared images were obtained with the ISAAC instrument at the ESO VLT in the Js, H and Ks bands reaching, respectively, 23.5, 22.0, 22.0 limiting Vega-magnitude. A multi-color (F300, F450, F606, F814, Js, H, Ks) photometric catalog of the HDF-S has been produced. Photometric redshifts have been generated both fitting templates to the observed SEDs and with neural network techniques. Spectroscopic observations of the 9 candidates with I_AB <24.25 have confirmed all of them to be galaxies with 2<z<3.5. The photometric redshifts for all the galaxies brighter than I_AB< 27.5 have been used to study the evolution of galaxy clustering in the interval 0<z<4.5.Comment: 2 pages Latex, To appear in the proceedings of "The mass of galaxies at low and high redshift", Venice, Oct 24-26, 2001,eds. R. Bender and A. Renzini (ESO Astrophysics Symposia, Springer-Verlag

The absorption spectrum of the QSO PKS 2126-158 (z_em = 3.27) at high resolution

Spectra of the z_em = 3.268 quasar PKS 2126-158 have been obtained in the range lambda lambda 4300-6620 A with a resolution R = 27000 and an average signal-to-noise ratio s/n = 25 per resolution element. The list of the identified absorption lines is given together with their fitted column densities and Doppler widths. The modal value of the Doppler parameter distribution for the Ly-alpha lines is = 25 km/s. The column density distribution can be described by a power-law dn/dN \propto N^{-beta} with beta = 1.5. 12 metal systems have been identified, two of which were previously unknown. In order to make the column densities of the intervening systems compatible with realistic assumptions about the cloud sizes and the silicon to carbon overabundance, it is necessary to assume a jump beyond the He II edge in the spectrum of the UV ionizing background at z = 3 a factor 10 larger than the standard predictions for the integrated quasar contribution. An enlarged sample of C IV absorptions (71 doublets) has been used to analyze the statistical properties of this class of absorbers strictly related to galaxies. The column density distribution is well described by a single power-law, with beta=1.64 and the Doppler parameter distribution shows a modal value b = 14 km/s. The two point correlation function has been computed in the velocity space for the individual components of C IV features. A significant signal is obtained for scales smaller than 200-300 km/s, xi(30< Delta v < 90 km/s) = 32.71 +- 2.89. A trend of decreasing clustering amplitude with decreasing column density is apparent, analogously to what has been observed for Ly-alpha lines.Comment: 16 pages, LaTeX (l-aa.sty), 13 ps figures, included in text with epsf, Fig. 1 can be retrieved at http://www.sissa.it/~dodorico/paper.html, accepted by Astronomy and Astrophysic

Changing the Age-old Stigmatization of Mental Health

For years, the importance of mental health has been overlooked. In the past, individuals possessing unstable mental health were not only neglected, but were highly stigmatized. In the 20th century, these individuals were thought to have demonic roots—they were feared. The mentally ill have been institutionalized, deinstitutionalized, and institutionalized yet again. Some progress has been made in changing society’s perceptions and fierce stigmatization of mental health. There are many organizations in place today aimed at increasing awareness and reducing stigmatization, and they have helped, but not nearly enough. Mental health stigmatization has detrimental effects on those that fall victim to it—ridding our society of this cruel stigmatization is long overdue. Stigmatization, especially the long-standing stigmatization of mental health, is not easy to undo. While prior research has shown that contact with mentally ill and mentally unstable individuals, as well as organized protests against mental health stigma, can be effective means of diminishing mental health stigmatization, the most effective means has been education. Research has also shown that over 25% of adults between ages 18 and 24 have a mental illness. This makes many college age individuals vulnerable to mental instability and makes seeking treatment during the college years essential. However, 40% of college students with mental health conditions don’t seek help, often because of stigma. Knowing this information, I’ve decided to create a new college course aimed at contributing to changing this age-old stigmatization of mental health. This proposed course is intended to provide students with a broad overview of the history and development of mental health and mental health stigma, the portrayal of mental health in the media, the significance of mental health in the criminal justice system, and the prevalence of mental health issues and stigma on college campuses. This course is intended to count for major-specific credit for all psychology majors, but also for general education credit, as all university students are encouraged to take the course. The course uniquely entails a project designed to familiarize students with the portrayal of mental health and mental illness in the media. The course also includes a project intended to garner appreciation for highly stigmatized individuals through experiential interaction. I’ve created samples of each portion of the course including a syllabus explicitly detailing the course, a sample lecture about mental health on college campuses, sample exam questions which complement the lecture, and an updated curriculum sheet showing where the course fits into existing curriculum requirements. Should this course be implemented, I hope that it would reduce mental health stigmatization, and normalize seeking help for mental instability, on college campuses. I designed this new course to be the course I wish I could have taken during my time as an undergraduate student. I tried my best to emphasize the important topics that were not as heavily emphasized in the core psychology courses. I also aimed to make this a course that all students would be interested in taking, regardless of their major. This was of the utmost importance to me because often, those undergraduate students that are psychology majors are already more sensitive, and aware, of mental health and the stigmatization that those with mental illnesses face—it’s the rest of the undergraduate population that could benefit, exponentially, from a course like this. At the end of the day, not enough is being done to combat mental health stigma, especially on college campuses. This is slowly improving, however, and I hope to see more colleges establishing programs and courses, such as this one, to aid in changing the age-old stigmatization of mental health. Presenting this poster, and a semester’s worth of hard work, at the Honors Conference was an incredible experience. Sharing my project allowed me the opportunity to talk the ear off many interested attendees about my favorite academic topics. It didn\u27t feel, in the least, like I was presenting a project. To me, I was simply sharing my deepest and most passionate interests. The conversations I had also truly exemplified just how much I want to see this course implemented. One of the many individuals I spoke to during the conference was the Chair of the Undergraduate Committee in Psychology, Dr. Patricia Morokoff. She expressed interest in seeing my course implemented as a Grand Challenge course, and I could not be more excited about this possibility