Rolf Arthur Jansen

Spectroscopic Discovery of the Supernova 2003dh Associated with GRB 030329

We present early observations of the afterglow of GRB 030329 and the spectroscopic discovery of its associated supernova SN 2003dh. We obtained spectra of the afterglow of GRB 030329 each night from March 30.12 (0.6 days after the burst) to April 8.13 (UT) (9.6 days after the burst). The spectra cover a wavelength range of 350-850 nm. The early spectra consist of a power-law continuum (Fν ν-0.9) with narrow emission lines originating from H II regions in the host galaxy, indicating a low redshift of z = 0.1687. However, our spectra taken after 2003 April 5 show broad peaks in flux characteristic of a supernova. Correcting for the afterglow emission, we find that the spectrum of the supernova is remarkably similar to the Type Ic hypernova SN 1998bw. While the presence of supernovae has been inferred from the light curves and colors of gamma-ray burst afterglows in the past, this is the first direct, spectroscopic confirmation that a subset of classical gamma-ray bursts originate from supernovae.

BVRI Light Curves for 22 Type 1a Supernovae

We present 1210 Johnson/Cousins B, V, R, and I photometric observations of 22 recent Type Ia supernovae (SNe Ia): SNe 1993ac, 1993ae, 1994M, 1994S, 1994T, 1994Q, 1994ae, 1995D, 1995E, 1995al, 1995ac, 1995ak, 1995bd, 1996C, 1996X, 1996Z, 1996ab, 1996ai, 1996bk, 1996bl, 1996bo, and 1996bv. Most of the photometry was obtained at the Fred Lawrence Whipple Observatory of the Harvard-Smithsonian Center for Astrophysics in a cooperative observing plan aimed at improving the database for SNe Ia. The redshifts of the sample range from cz = 1200 to 37,000 km s-1 with a mean of cz = 7000 km s-1.

OII) AS A STAR FORMATION RATE INDICATOR

We investigate the [O II] emission line as a star formation rate (SFR) indicator using integrated spectra of 97 galaxies from the Nearby Field Galaxies Survey (NFGS). The sample includes all Hubble types and contains SFRs ranging from 0.01 to 100 M⊙ yr-1. We compare the Kennicutt [O II] and Hα SFR calibrations and show that there are two significant effects that produce disagreement between SFR([O II]) and SFR(Hα): reddening and metallicity. Differences in the ionization state of the interstellar medium do not contribute significantly to the observed difference between SFR([O II]) and SFR(Hα) for the NFGS galaxies with metallicities log (O/H) + 12 8.5. The Kennicutt [O II]-SFR relation assumes a typical reddening for nearby galaxies; in practice, the reddening differs significantly from sample to sample. We derive a new SFR([O II]) calibration that does not contain a reddening assumption. Our new SFR([O II]) calibration also provides an optional correction for metallicity. Our SFRs derived from [O II] agree with those derived from Hα to within 0.03–0.05 dex. We show that the reddening, E(B-V), increases with intrinsic (i.e., reddening-corrected) [O II] luminosity for the NFGS sample. We apply our SFR([O II]) calibration with metallicity correction to two samples: high-redshift 0.8 < z < 1.6 galaxies from the NICMOS Hα survey and 0.5 < z < 1.1 galaxies from the Canada-France Redshift Survey. The SFR([O II]) and SFR(Hα) for these samples agree to within the scatter observed for the NFGS sample, indicating that our SFR([O II]) relation can be applied to both local and high-z galaxies. Finally, we apply our SFR([O II]) to estimates of the cosmic star formation history. After reddening and metallicity corrections, the star formation rate densities derived from [O II] and Hα agree to within ~30%.

Photometry and Spectroscopy of GRB 030329 and Its Associated Supernova 2003dh: The First Two Months

We present extensive optical and infrared photometry of the afterglow of gamma-ray burst (GRB) 030329 and its associated supernova (SN) 2003dh over the first two months after detection (2003 March 30-May 29 UT). Optical spectroscopy from a variety of telescopes is shown and, when combined with the photometry, allows an unambiguous separation between the afterglow and SN contributions. The optical afterglow of the GRB is initially a power-law continuum but shows significant color variations during the first week that are unrelated to the presence of an SN. The early afterglow light curve also shows deviations from the typical power-law decay. An SN spectrum is first detectable ~7 days after the burst and dominates the light after ~11 days. The spectral evolution and the light curve are shown to closely resemble those of SN 1998bw, a peculiar Type Ic SN associated with GRB 980425, and the time of the SN explosion is close to the observed time of the GRB. It is now clear that at least some GRBs arise from core-collapse SNe.

Aperture effects on star formation rate, metallicity and reddening

ABSTRACT We use 101 galaxies selected from the Nearby Field Galaxy Survey to investigate the effect of aperture size on the star formation rate, metallicity, and reddening determinations for galaxies. Our sample includes galaxies of all Hubble types except ellipticals with global star formation rates (SFRs) ranging from 0.01 to 100 M⊙ yr−1, metallicities in the range \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Spectrophotometry of Nearby Field Galaxies: The Data

7.9\lesssim \mathrm{log}\,( \mathrm{O}\,/ \mathrm{H}\,) +12\lesssim 9.0

The H-alpha and infrared star formation rates for the nearby field galaxy survey

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[O II] As a Tracer of Current Star Formation

We have obtained integrated and nuclear spectra as well as U, B, R surface photometry for a representative sample of 196 nearby galaxies. These galaxies span the entire Hubble sequence in morphological type, as well as a wide range of luminosities (MB = -14 to -22). Here we present the spectrophotometry for these galaxies. The selection of the sample and the U, B, R surface photometry is described in a companion paper. Our goals for the project include measuring the current star formation rates and metallicities of these galaxies, and elucidating their star formation histories, as a function of luminosity and morphology. We thereby extend the work of Kennicutt to lower luminosity systems. We anticipate that our study will be useful as a benchmark for studies of galaxies at high redshift. We describe the observing, data reduction, and calibration techniques and demonstrate that our spectrophotometry agrees well with that of Kennicutt. The spectra span the range 3550-7250 A at a resolution (FWHM) of ~6 A and have an overall relative spectrophotometric accuracy of ~±6%. We present a spectrophotometric atlas of integrated and nuclear rest-frame spectra as well as tables of equivalent widths and synthetic colors. The atlas and tables of measurements will be made available electronically. We study the correlations of galaxy properties determined from the spectra and images. Our findings include: (1) galaxies of a given morphological class display a wide range of continuum shapes and emission-line strengths if a broad range of luminosities are considered, (2) emission-line strengths tend to increase and continua tend to get bluer as the luminosity decreases, and (3) the scatter on the general correlation between nuclear and integrated Hα emission-line strengths is large.

Surface photometry of nearby field galaxies: The data

We investigate the Hα and infrared star formation rate (SFR) diagnostics for galaxies in the Nearby Field Galaxy Survey (NFGS). For the 81 galaxies in our sample, we derive Hα fluxes (included here) from integrated spectra. There is a strong correlation between the ratio of far-infrared to optical luminosities L(FIR)/L(Hα) and the extinction E(B-V) measured with the Balmer decrement. Before reddening correction, the SFR(IR) and SFR(Hα) are related to each other by a power law: SFR(IR) = (2.7 ± 0.3)SFR(Hα)1.30±0.06. Correction of the SFR(Hα) for extinction using the Balmer decrement and a classical reddening curve both reduces the scatter in the SFR(IR)-SFR(Hα) correlation and results in a much closer agreement between the two SFR indicators; SFR(IR) = (0.91 ± 0.04)SFR(Hαcorr)1.07±0.03. SFR(IR) and SFR(Hα) agree to ~10%. This SFR relationship spans 4 orders of magnitude and holds for all Hubble types with IRAS detections in the NFGS. A constant ratio between the SFR(IR) and SFR(Hα) for all Hubble types, including early types (S0–Sab), suggests that the IR emission in all these objects results from a young stellar population.

Ubvr and hubble space telescope mid-ultraviolet and near-infrared surface photometry and radial color gradients of late-type, irregular, and peculiar galaxies

[O II] lambda 3727 is often used as a tracer of star formation at intermediate redshifts (z greater than or similar to 0.4), where H alpha is not easily observed. We use the spectrophotometric data of the Nearby Field Galaxy Survey to investigate the range and systematic variation in the observed [O II]/H alpha emission-line ratio as a function of galaxy luminosity at low redshift. We find that the observed [O II]/H alpha ratio varies by a factor of 7 at luminosities near M-B*. The [O II]/H alpha ratio is inversely correlated with luminosity. The scatter in the [O II]/H alpha ratio and the dependence of the ratio on luminosity are due in equal parts to reddening and to the metallicity-dependent excitation of the interstellar medium. The uncertainty in star formation rates derived from [O II] fluxes is therefore large. If H alpha cannot be observed, high signal-to-noise ratio H beta fluxes are much preferable to [O II] fluxes for deriving star formation rates. We present several purely empirical corrections for extinction.