Optical Photometry of the Type Ia SN 1999ee and the Type Ib/c SN 1999ex in IC 5179

We present UBVRIz lightcurves of the Type Ia SN 1999ee and the Type Ib/c SN 1999ex, both located in the galaxy IC 5179. SN 1999ee has an extremely well sampled lightcurve spanning from 10 days before Bmax through 53 days after peak. Near maximum we find systematic differences ~0.05 mag in photometry measured with two different telescopes, even though the photometry is reduced to the same local standards around the supernova using the specific color terms for each instrumental system. We use models for our bandpasses and spectrophotometry of SN 1999ee to derive magnitude corrections (S-corrections) and remedy this problem. This exercise demonstrates the need of accurately characterizing the instrumental system before great photometric accuracies of Type Ia supernovae can be claimed. It also shows that this effect can have important astrophysical consequences since a small systematic shift of 0.02 mag in the B-V color can introduce a 0.08 mag error in the extinction corrected peak B magnitudes of a supernova and thus lead to biased cosmological parameters. The data for the Type Ib/c SN 1999ex present us with the first ever observed shock breakout of a supernova of this class. These observations show that shock breakout occurred 18 days before Bmax and support the idea that Type Ib/c supernovae are due to core collapse of massive stars rather than thermonuclear disruption of white dwarfs.Comment: 55 pages, 15 figures, accepted by the Astronomical Journa

The observable supernova rate in galaxy–galaxy lensing systems with the TESS satellite

The Transiting Exoplanet Survey Satellite (TESS) is the latest observational effort to find exoplanets and map bright transient optical phenomena. Supernovae (SNe) are particularly interesting as cosmological standard candles for cosmological distance measures. The limiting magnitude of TESS strongly constrains SN detection to the very nearby Universe (m ∼ 19, z \u3c 0.05). We explore the possibility that more distant SNe that are gravitationally lensed and magnified by a foreground galaxy can be detected by TESS, an opportunity to measure the time delay between light paths and constrain the Hubble constant independently. We estimate the rate of occurrence of such systems, assuming reasonable distributions of magnification, host dust attenuation, and redshift. There are approximately 16 Type Ia SNe (SNIa) and 43 core-collapse SNe (SNcc) expected to be observable with TESS each year, which translates to 18 and 43 per cent chance of detection per year, respectively. Monitoring the largest collections of known strong galaxy–galaxy lenses from Petrillo et al., this translates into 0.6 and 1.3 per cent chances of an SNIa and an SNcc per year. The TESS all-sky detection rates are lower than those of the Zwicky Transient Facility and Vera Rubin Observatory. However, on the ecliptic poles, TESS performs almost as well as its all-sky search, thanks to its continuous coverage: 2 and 4 per cent chance of an observed SN (Ia or cc) each year. These rates argue for timely processing of full-frame TESS imaging to facilitate follow-up and should motivate further searches for low-redshift lensing system

Helium and Iron in X-ray galaxy clusters

I discuss the role of the sedimentation of helium in galaxy cluster cores on the observed X-ray properties and present a history of the metal accumulation in the ICM, with new calculations with respect to my previous work following the recent evidence of a bi-modal distribution of the delay time in Supernovae Type Ia.Comment: 6 pages. To appear in the Proceedings of "Heating vs. Cooling in Galaxies and Clusters of Galaxies", August 2006, Garching (Germany

Did Galaxy Assembly and Supermassive Black-Hole Growth go hand-in-hand?

In this paper, we address whether the growth of supermassive black-holes has kept pace with the process of galaxy assembly. For this purpose, we first searched the Hubble Ultra Deep Field (HUDF) for "tadpole galaxies", which have a knot at one end and an extended tail. They appear dynamically unrelaxed -- presumably early-stage mergers -- and make up ~6% of the field galaxy population. Their redshift distribution follows that of field galaxies, indicating that -- if tadpole galaxies are indeed dynamically young -- the process of galaxy assembly generally kept up with the reservoir of field galaxies as a function of epoch. Next, we present a search for HUDF objects with point-source components that are optically variable (at the >~3.0 sigma level) on timescales of weeks--months. Among 4644 objects to i_AB=28.0 mag (10 sigma), 45 have variable point-like components, which are likely weak AGN. About 1% of all field objects show variability for 0.1 < z < 4.5, and their redshift distribution is similar to that of field galaxies. Hence supermassive black-hole growth in weak AGN likely also kept up with the process of galaxy assembly. However, the faint AGN sample has almost no overlap with the tadpole sample, which was predicted by recent hydrodynamical numerical simulations. This suggests that tadpole galaxies are early-stage mergers, which likely preceded the ``turn-on'' of the AGN component and the onset of visible point-source variability by >~1 Gyr.Comment: 9 pages, Latex2e requires 'elsart' and 'elsart3' (included), 10 postscript figures. To appear in the Proceedings of the Leiden Workshop on "QSO Host Galaxies: Evolution and Environment", eds. P.D. Barthel & D.B. Sanders (New Astron. Rev., 2006

Clues to AGN Growth from Optically Variable Objects in the Hubble Ultra Deep Field

We present a photometric search for objects with point-source components that are optically variable on timescales of weeks--months in the Hubble Ultra Deep Field (HUDF) to i'(AB)=28.0 mag. The data are split into four sub-stacks of approximately equal exposure times. Objects exhibiting the signature of optical variability are selected by studying the photometric error distribution between the four different epochs, and selecting 622 candidates as 3.0 sigma outliers from the original catalog of 4644 objects. Of these, 45 are visually confirmed as free of contamination from close neighbors or various types of image defects. Four lie within the positional error boxes of Chandra X-ray sources, and two of these are spectroscopically confirmed AGN. The photometric redshift distribution of the selected variable sample is compared to that of field galaxies, and we find that a constant fraction of ~1% of all field objects show variability over the range of 0.1<z<4.5. Combined with other recent HUDF results, as well as those of recent state-of-the-art numerical simulations, we discuss a potential link between the hierarchical merging of galaxies and the growth of AGN.Comment: 9 pages, 6 figures, accepted for publication in Astrophysical Journal, minor changes to reference

SN Refsdal: Classification as a Luminous and Blue SN 1987A-like Type II Supernova

We have acquired Hubble Space Telescope (HST) and Very Large Telescope near-infrared spectra and images of supernova (SN) Refsdal after its discovery as an Einstein cross in Fall 2014. The HST light curve of SN Refsdal matches the distinctive, slowly rising light curves of SN 1987A-like supernovae (SNe), and we find strong evidence for a broad H-alpha P-Cygni profile in the HST grism spectrum at the redshift (z = 1.49) of the spiral host galaxy. SNe IIn, powered by circumstellar interaction, could provide a good match to the light curve of SN Refsdal, but the spectrum of a SN IIn would not show broad and strong H-alpha absorption. From the grism spectrum, we measure an H-alpha expansion velocity consistent with those of SN 1987A-like SNe at a similar phase. The luminosity, evolution, and Gaussian profile of the H-alpha emission of the WFC3 and X-shooter spectra, separated by ~2.5 months in the rest frame, provide additional evidence that supports the SN 1987A-like classification. In comparison with other examples of SN 1987A-like SNe, SN Refsdal has a blue B-V color and a high luminosity for the assumed range of potential magnifications. If SN Refsdal can be modeled as a scaled version of SN 1987A, we estimate it would have an ejecta mass of 20+-5 solar masses. The evolution of the light curve at late times will provide additional evidence about the potential existence of any substantial circumstellar material (CSM). Using MOSFIRE and X-shooter spectra, we estimate a subsolar host-galaxy metallicity (8.3+-0.1 dex and <8.4 dex, respectively) near the explosion site.Comment: Submitted to ApJ; 26 page