سمینار این هفته را خانم غزاله عرفانیانفر از دانشگاه فنی مونیخ  (Excellence Cluster Universe) ارائه  خواهند کرد. عنوان و چکیدهٔ سمینار ایشان به شرح زیر است:

اثر محیط در تغییر فعالیت ستاره زایی کهکشان ها

 (Environmental dependence of star forming galaxies)

Abstract: The level of star formation (SF) activity in galaxy systems is known to be suppressed relative to the field. According to the well known morphology-density relation and the star formation rate-density relation, in the local Universe high density regions, like groups and clusters, host mostly early type galaxies with lower SF level than field (mostly late-type) galaxies. The environmental dependence of galaxy SF rate may change with redshift, as galaxies in systems undergo significant evolution. Why to study groups in this context? What emerges from recent results is that the largest contribution to the the star formation rate density of the Universe is provided by rather massive galaxies (10^10 -10^11Msun). Galaxy groups host 70% of massive galaxies at least up to redshift ~1. Thus, it is likely that, if SF rate quenching happens in high density regions, those must be galaxy groups. Thus, to obtain a complete census of the group galaxy population at stellar mass larger than 10^10 Msun and of their star formation activity up to redshift ~1, we create a statistical sample of X-ray selected groups up to z~1 in the major blank fields (AEGIS, COSMOS, CDFN and ECDFS) observed also by the infrared Herschel satellite. We observe a clear evolution in the level of star formation activity in galaxy groups. The total star formation activity in high redshift groups (0.5<z<1) is higher with respect to the low redshift (0.15<z<0.5) sample at any mass by 0.8±0.12 dex.  We also analyse the dependence of environments on the position of galaxies in the star formation rate (SFR) versus stellar mass diagram. We distinguish lower halo mass environments based on the local galaxy density. We find that Main Sequence (MS) of star forming galaxies is not a linear relation and there is a flattening towards higher stellar masses ( Msun > 10^10.4Msun). The flattening exists in all environmental classes. All environments have almost the same MS at high redshifts (0.5<z<1.1) while group galaxies tend to deviate from the mean MS towards the region of quiescence with respect to other environments in low redshifts (0.15<z<0.5). Our results suggest group galaxies evolve in a much faster way with respect to galaxies in lower mass halos in terms of quenching of the SF activity.

این سمینار در روز یکشنبه ۱۲ بهمن ماه ۱۳۹۳، ساعت ۱۵ در کلاس فیزیک ۴ در طبقه اول  دانشکدهٔ فیزیک برگزار خواهد شد.