Roth et al. (2014a) reported evidence for plumes of water venting from a southern high latitude region on Europa: spectroscopic detection of off-limb line emission from the dissociation products of ...water. Here, we present Hubble Space Telescope direct images of Europa in the far-ultraviolet (FUV) as it transited the smooth face of Jupiter to measure absorption from gas or aerosols beyond the Europa limb. Out of 10 observations, we found 3 in which plume activity could be implicated. Two observations showed statistically significant features at latitudes similar to Roth et al., and the third at a more equatorial location. We consider potential systematic effects that might influence the statistical analysis and create artifacts, and are unable to find any that can definitively explain the features, although there are reasons to be cautious. If the apparent absorption features are real, the magnitude of implied outgassing is similar to that of the Roth et al. feature; however, the apparent activity appears more frequently in our data.
Using three magnified Type Ia supernovae (SNe Ia) detected behind CLASH (Cluster Lensing and Supernovae with Hubble) clusters, we perform a first pilot study to see whether standardizable candles can ...be used to calibrate cluster mass maps created from strong lensing observations. Such calibrations will be crucial when next-generation Hubble Space Telescope cluster surveys (e.g. Frontier) provide magnification maps that will, in turn, form the basis for the exploration of the high-redshift Universe. We classify SNe using combined photometric and spectroscopic observations, finding two of the three to be clearly of Type Ia and the third probable. The SNe exhibit significant amplification, up to a factor of 1.7 at ... significance (SN-L2). We conducted this as a blind study to avoid fine-tuning of parameters, finding a mean amplification difference between SNe and the cluster lensing models of 0.09 ± 0.09stat ± 0.05sys mag. This impressive agreement suggests no tension between cluster mass models and high-redshift-standardized SNe Ia. However, the measured statistical dispersion of ... = 0.21 mag appeared large compared to the dispersion expected based on statistical uncertainties (0.14). Further work with the SN and cluster lensing models, post-unblinding, reduced the measured dispersion to ... = 0.12. An explicit choice should thus be made as to whether SNe are used unblinded to improve the model, or blinded to test the model. As the lensed SN samples grow larger, this technique will allow improved constraints on assumptions regarding e.g. the structure of the dark matter halo. (ProQuest: ... denotes formulae/symbols omitted.)
AGN Feedback Driven Molecular Outflow in NGC 1266 Alatalo, K.; Nyland, K. E.; Graves, G. ...
Proceedings of the International Astronomical Union,
08/2012, Letnik:
8, Številka:
S290
Journal Article
Recenzirano
Odprti dostop
NGC 1266 is a nearby field galaxy observed as part of the ATLAS3D survey (Cappellari et al. 2011). NGC 1266 has been shown to host a compact (< 200 pc) molecular disk and a mass-loaded molecular ...outflow driven by the AGN (Alatalo et al. 2011). Very Long Basline Array (VLBA) observations at 1.65 GHz revealed a compact (diameter < 1.2 pc), high brightness temperature continuum source most consistent with a low-level AGN origin. The VLBA continuum source is positioned at the center of the molecular disk and may be responsible for the expulsion of molecular gas in NGC 1266. Thus, the candidate AGN-driven molecular outflow in NGC 1266 supports the picture in which AGNs do play a significant role in the quenching of star formation and ultimately the evolution of the red sequence of galaxies.
We detail the rich molecular story of NGC 1266, its serendipitous discovery within the ATLAS3D survey (Cappellari et al. 2011) and how it plays host to an AGN-driven molecular outflow, potentially ...quenching all of its star formation (SF) within the next 100 Myr. While major mergers appear to play a role in instigating outflows in other systems, deep imaging of NGC 1266 as well as stellar kinematic observations from SAURON, have failed to provide evidence that NGC 1266 has recently been involved in a major interaction. The molecular gas and the instantaneous SF tracers indicate that the current sites of star formation are located in a hypercompact disk within 200 pc of the nucleus (Fig. 1; SF rate ≈ 2 M⊙ yr−1). On the other hand, tracers of recent star formation, such as the Hβ absorption map from SAURON and stellar population analysis show that the young stars are distributed throughout a larger area of the galaxy than current star formation. As the AGN at the center of NGC 1266 continues to drive cold gas out of the galaxy, we expect star formation rates to decline as the star formation is ultimately quenched. Thus, NGC 1266 is in the midst of a key portion of its evolution and continued studies of this unique galaxy may help improve our understanding of how galaxies transition from the blue to the red sequence (Alatalo et al. 2011).
The Type Ia Supernova Rate at z ~ 0.4 Pain, R; Hook, I. M; Deustua, S ...
Astrophysical journal/The Astrophysical journal,
12/1996, Letnik:
473, Številka:
1
Journal Article
We develop a method to measure the strength of the absorption features in type Ia supernova (SN Ia) spectra and use it to make a quantitative comparisons between the spectra of type Ia supernovae at ...low and high redshifts. In this case study, we apply the method to 12 high-redshift (0.212 ≤ z ≤ 0.912) SNe Ia observed by the Supernova Cosmology Project. Through measurements of the strengths of these features and of the blueshift of the absorption minimum in Ca ii H&K, we show that the spectra of the high-redshift SNe Ia are quantitatively similar to spectra of nearby SNe Ia (z < 0.15). One supernova in our high redshift sample, SN 2002fd at z = 0.279, is found to have spectral characteristics that are associated with peculiar SN 1991T/SN 1999aa-like supernovae.
Type Ia Supernovae (SNe Ia) are powerful standardizable candles for constraining cosmological models and provided the first evidence of the accelerated expansion of the universe. Their precision ...derives from empirical correlations, now measured from \(>1000\) SNe Ia, between their luminosities, light-curve shapes, colors and most recently with the stellar mass of their host galaxy. As mass correlates with other galaxy properties, alternative parameters have been investigated to improve SN Ia standardization though none have been shown to significantly alter the determination of cosmological parameters. We re-examine a recent claim, based on 34 SN Ia in nearby passive host galaxies, of a 0.05 mag/Gyr dependence of standardized SN Ia luminosity on host age which if extrapolated to higher redshifts, would be a bias up to 0.25 mag, challenging the inference of dark energy. We reanalyze this sample of hosts using both the original method and a Bayesian hierarchical model and find after a fuller accounting of the uncertainties the significance of a dependence on age to be \(\leq2\sigma\) and \(\sim1\sigma\) after the removal of a single poorly-sampled SN Ia. To test the claim that a trend seen in old stellar populations can be applied to younger ages, we extend our analysis to a larger sample which includes young hosts. We find the residual dependence of host age (after all standardization typically employed for cosmological measurements) to be consistent with zero for 254 SNe Ia from the Pantheon sample, ruling out the large but low significance trend seen in passive hosts.
We present VLT FORS1 and FORS2 spectra of 39 candidate high-redshift supernovae that were discovered as part of a cosmological study using type Ia supernovae (SNe Ia) over a wide range of redshifts. ...From the spectra alone, 20 candidates are spectrally classified as SNe Ia with redshifts ranging from z = 0.212 to z = 1.181. Of the remaining 19 candidates, 1 might be a type II supernova and 11 exhibit broad supernova-like spectral features and/or have supernova-like light curves. The candidates were discovered in 8 separate ground-based searches. In those searches in which SNe Ia at z similar to 0.5 were targeted, over 80% of the observed candidates were spectrally classified as SNe Ia. In those searches in which SNe Ia with z > 1 were targeted, 4 candidates with z > 1 were spectrally classified as SNe Ia and later followed with ground and space based observatories. We present the spectra of all candidates, including those that could not be spectrally classified as supernova.
This note presents an initial survey design for the Nancy Grace Roman High-latitude Time Domain Survey. This is not meant to be a final or exhaustive list of all the survey strategy choices, but ...instead presents a viable path towards achieving the desired precision and accuracy of dark energy measurements using Type Ia supernovae (SNe Ia). We describe a survey strategy that use six filters (RZYJH and F) and the prism on the Roman Wide Field Instrument. This survey has two tiers, one "wide" which targets SNe Ia at redshifts up to 1 and one "deep" targeting redshifts up to 1.7; for each, four filters are used (with Y and J used in both tiers). We propose one field each in the north and south continuous viewing zones, and expect to obtain high-quality distances of \(\sim\)12,000 SNe Ia with \(\sim\)5,000 at z > 1. We propose a wide-tier area of \(\sim\)19 deg\(^2\) and a deep tier of \(\sim\)5 deg\(^2\). Exposure times range from 100 s to 900 s for imaging and 900 s to 3600 s for the prism. These exposure times would reach \(\sim\)25.5 mag and \(\sim\)26.5 mag for the wide and deep tiers respectively, with deep co-add stacks reaching \(\sim\)28 mag and \(\sim\)29 mag. The total survey spans two years, with a total allocation time of six months, and a cadence of \(\sim\)5 days.
PDF
