31 research outputs found
Probing the Star Formation History and Initial Mass Function of the z~2.5 Lensed Galaxy SMM J163554.2+661225 with Herschel
We present the analysis of Herschel SPIRE far-infrared (FIR) observations of
the z = 2.515 lensed galaxy SMM J163554.2+661225. Combining new 250, 350, and
500 micron observations with existing data, we make an improved fit to the FIR
spectral energy distribution (SED) of this galaxy. We find a total infrared
(IR) luminosity of L(8--1000 micron) = 6.9 +/- 0.6x10^11 Lsol; a factor of 3
more precise over previous L_IR estimates for this galaxy, and one of the most
accurate measurements for any galaxy at these redshifts. This FIR luminosity
implies an unlensed star formation rate (SFR) for this galaxy of 119 +/- 10
Msol per yr, which is a factor of 1.9 +/- 0.35 lower than the SFR derived from
the nebular Pa-alpha emission line (a 2.5-sigma discrepancy). Both SFR
indicators assume identical Salpeter initial mass functions (IMF) with slope
Gamma=2.35 over a mass range of 0.1 - 100 Msol, thus this discrepancy suggests
that more ionizing photons may be necessary to account for the higher
Pa-alpha-derived SFR. We examine a number of scenarios and find that the
observations can be explained with a varying star formation history (SFH) due
to an increasing star formation rate (SFR), paired with a slight flattening of
the IMF. If the SFR is constant in time, then larger changes need to be made to
the IMF by either increasing the upper-mass cutoff to ~ 200 Msol, or a
flattening of the IMF slope to 1.9 +/- 0.15, or a combination of the two. These
scenarios result in up to double the number of stars with masses above 20 Msol,
which produce the requisite increase in ionizing photons over a Salpeter IMF
with a constant SFH.Comment: 9 pages, 4 figures, 1 table; Accepted for publication in the
Astrophysical Journa
Turning Back the Clock: Inferring the History of the Eight O'clock Arc
We present the results from an optical and near-infrared spectroscopic study
of the ultraviolet-luminous z = 2.73 galaxy, the 8 o'clock arc. Due to
gravitational lensing, this galaxy is magnified by a factor of > 10, allowing
in-depth measurements which are usually unfeasible at such redshifts. In the
optical spectra, we measured the systemic redshift of the galaxy, z = 2.7322
+/- 0.0012, using stellar photospheric lines. This differs from the redshift of
absorption lines in the interstellar medium, z = 2.7302 +/- 0.0006, implying
gas outflows on the order of 160 km/s. With H and K-band near-infrared spectra,
we have measured nebular emission lines of Halpha, Hbeta, Hgamma, [N II] and [O
III], which have a redshift z = 2.7333 +/- 0.0001, consistent with the derived
systemic redshift. From the Balmer decrement, we measured the dust extinction
to be A_5500 = 1.17 +/- 0.36 mag. Correcting Halpha for dust extinction and the
assumed lensing factor, we measure a star-formation rate of ~ 270 Msol/yr,
which is higher than ~ 85% of star-forming galaxies at z ~ 2-3. Using
combinations of all detected emission lines, we find that the 8 o'clock arc has
a gas-phase metallicity of ~ 0.8 Zsol, showing that enrichment at high-redshift
is not rare, even in blue, star-forming galaxies. Studying spectra from two of
the arc components separately, we find that one component dominates the dust
extinction and star-formation rate, although the metallicities between the two
components are similar. We derive the mass via stellar population modeling, and
find that the arc has a total stellar mass of ~ 4 x 10^11 Msol, which falls on
the mass-metallicity relation at z ~ 2. Finally, we estimate the total gas
mass, and find it to be only ~ 12% of the stellar mass, implying that the 8
o'clock arc is likely nearing the end of a starburst.Comment: Replaced with updated version after proofs. SFR and A_V values have
been update
Paschen-alpha Emission in the Gravitationally Lensed Galaxy SMM J163554.2+661225
We report the detection of the Paschen-alpha emission line in the z=2.515
galaxy SMM J163554.2+661225 using Spitzer spectroscopy. SMM J163554.2+661225 is
a sub-millimeter-selected infrared (IR)-luminous galaxy maintaining a high
star-formation rate (SFR), with no evidence of an AGN from optical or infrared
spectroscopy, nor X-ray emission. This galaxy is lensed gravitationally by the
cluster Abell 2218, making it accessible to Spitzer spectroscopy. Correcting
for nebular extinction derived from the H-alpha and Pa-alpha lines, the
dust-corrected luminosity is L(Pa-alpha) = (2.57+/-0.43) x 10^43 erg s^-1,
which corresponds to an ionization rate, Q = (1.6+/-0.3) x 10^55 photons s^-1.
The instantaneous SFR is 171+/-28 solar masses per year, assuming a
Salpeter-like initial mass function. The total IR luminosity derived using 70,
450, and 850 micron data is L(IR) = (5-10) x 10^11 solar luminosities,
corrected for gravitational lensing. This corresponds to a SFR=90-180 solar
masses per year, where the upper range is consistent with that derived from the
Paschen-alpha luminosity. While the L(8 micron) / L(Pa-alpha) ratio is
consistent with the extrapolated relation observed in local galaxies and
star-forming regions, the rest-frame 24 micron luminosity is significantly
lower with respect to local galaxies of comparable Paschen-alpha luminosity.
Thus, SMM J163554.2+661225 arguably lacks a warmer dust component (T ~ 70 K),
which is associated with deeply embedded star formation, and which contrasts
with local galaxies with comparable SFRs. Rather, the starburst is consistent
with star-forming local galaxies with intrinsic luminosities, L(IR) ~ 10^10
solar luminosities, but "scaled-up" by a factor of 10-100.Comment: Published in the Astrophysical Journal. 14 pages in emulateapj
format, 9 figures (many in color
College Women’s Feminist Identity: A Multidimensional Analysis with Implications for Coping with Sexism
Predicting Organizational Citizenship Behavior: Integrating the Functional and Role Identity Approaches
Motive and role identity, previously studied as predictors of volunteerism, were examined as correlates of another discretionary prosocial behavior, Organizational Citizenship Behavior (OCB). County employees (181 females, 62 males) completed questionnaires that measured frequency of OCB, motives for the behavior, and the degree to which the respondents had developed an organizational citizen identity. Motives concerned with the desire to help coworkers and/or the organization proved to be better predictors of OCB than those concerned with the desire for Impression Management. A citizen role identity also correlated with citizenship behavior but, contrary to expectation, mediated the relationship between OCB and motive only partly. The findings suggest that similar mechanisms are involved in sustaining both volunteerism and OCB
Dispositional and Structural Determinants of Volunteerism
The dispositional and structural correlates of volunteerism were examined in a panel study. AIDS service organization volunteers answered questions about affect toward the organization, organizational commitment, motives for volunteering, and a prosocial personality orientation. These measures were used to predict 4 volunteer-related behaviors. Length of service was weakly correlated with the 3 other volunteer behaviors. Altruistic motives and prosocial personality characteristics predicted several of the volunteer behaviors. Initial levels of volunteer activity and organizational commitment also predicted final levels of volunteer activity, but these effects were mediated through intermediate levels of volunteer activities. The findings are discussed within the context of the volunteer process model and role identity models of volunteerism
A Case for the Revision of Textbook Models of Color Vision: The Detection and Appearance of Small Brief Lights
Comparison of Changes in Sensitivity and Sensation: Implications for the Response-Intensity Function of the Human Photopic System
Brightness magnitude estimations of foveally presented flashes deviate from a power function. Increment threshold functions for test lights presented upon these same flashes deviate drastically from a constant Weber fraction. These departures from the classic laws of sensation and sensitivity are shown to be in qualitative agreement and to be affected in similar ways by changes in steady adapting fields. Both sets of data can be fit over the lower range of flash intensities by models based on a saturating response function; both sets deviate from these models at high flash intensities in ways consistent with a nonsaturating response function
Making Decisions about Condoms: Whose Attitude is it Anyway
Policy capturing was used to assess the relative influence of one\u27s own attitudes and those of a sexual partner on decisions about condoms. Participants read vignettes describing a romantic encounter between themselves and a hypothetical date. Each vignette contained 6 independent variables; 3 described aspects of the participant\u27s attitudes toward condoms, and 3 described the corresponding attitudes of the date. For each scenario, participants judged the likelihood that they would use a condom should they have intercourse. The decision was independently affected by the attitudes of both participant and date. A second experiment showed the date\u27s influence increasing with time constraints. The results suggest that efforts to increase condom use may require heightened awareness of the influence of the other\u27s attitude on decision-making