Search

A common challenge among university professors is how to best design undergraduate courses to successfully enhance students' attitudes. To compare which curriculum was more efficient at fostering a positive attitude towards science in general, I studied the impact of two different general education science courses on the attitudes of college students. The first course was an arithmetic-based Introductory Astronomy course for non-science majoring undergraduates that used interactive and inquiry-based teaching techniques. The comparison course was a Science, Technology, & Society (STS) seminar with context-based science contents, discussions, and intensive reading and writing. The post-semester results showed that neither curriculum on its own significantly changed the overall attitude of students towards science as far the assessment could measure, but that each curriculum did successfully enhance specific aspects of the students’ attitude in differing categories. The STS students had scores showing a gain in believing that scientists are honest. The astronomy students had scores showing a gain in understanding that scientific theories can change in the light of new evidence. However, the most significant change was a loss in the astronomy students’ confidence that the general public can and should understand science. Thus, the results suggest that professors who strongly desire to enhance the broad nature of students' attitudes need to use more purposeful instructional experiences rather than rely only on students' deepening understanding of the specific scientific content.

We present Gemini/GNIRS spectroscopy of the Seyfert 2 galaxy NGC 4388, with simultaneous coverage from 0.85 - 2.5 $\mu$m. Several spatially-extended emission lines are detected for the first time, both in the obscured and unobscured portion of the optical narrow line region (NLR), allowing us to assess the combined effects of the central continuum source, outflowing gas and shocks generated by the radio jet on the central 280 pc gas. The HI and [FeII] lines allow us to map the extinction affecting the NLR. We found that the nuclear region is heavily obscured, with E(B-V) ~1.9 mag. To the NE of the nucleus and up to ~150 pc, the extinction remains large, ~1 mag or larger, consistent with the system of dust lanes seen in optical imaging. We derived position-velocity diagrams for the most prominent lines as well as for the stellar component. Only the molecular gas and the stellar component display a well-organized pattern consistent with disk rotation. Other emission lines are kinematically perturbed or show little evidence of rotation. Extended high-ionization emission of sulfur, silicon and calcium is observed to distances of at least 200 pc both NE and SW of the nucleus. We compared flux ratios between these lines with photoionization models and conclude that radiation from the central source alone cannot explain the observed high-ionization spectrum. Shocks between the radio-jet and the ambient gas are very likely an additional source of excitation. We conclude that NGC 4388 is a prime laboratory to study the interplay between all these mechanisms., Comment: 21 pages, 14 figures, 9 tables. Accepted for publication in MNRAS

To investigate AGN outflows as a tracer of AGN feedback on star-formation, we perform integral-field spectroscopy of 20 type 2 AGNs at z10$^{41.5}$ erg/s, and exhibit strong outflow signatures in the [O III] kinematics. By decomposing the emission-line profile, we obtain the maps of the narrow and broad components of [O III] and H$\alpha$ lines, respectively. The broad components in both [O III] and H$\alpha$ represent the non-gravitational kinematics, i.e., gas outflows, while the narrow components, especially in H$\alpha$, represent the gravitational kinematics, i.e., rotational disk. By using the integrated spectra within the flux-weighted size of the narrow-line region, we estimate the energetics of the gas outflows. The ionized gas mass is 1.0-38.5$\times 10^5$ $M_{\odot}$, and the mean mass outflow rate is 4.6$\pm$4.3 $M_{\odot}$/yr, which is a factor of ~260 higher than the mean mass accretion rate 0.02$\pm$0.01 $M_{\odot}$/yr. The mean energy injection rate of the sample is 0.8$\pm$0.6% of the AGN bolometric luminosity, while the momentum flux is (5.4$\pm$3.6)$\times$ $L_{bol}$/c on average, except for two most kinematically energetic AGNs with low $L_{bol}$, which are possibly due to the dynamical timescale of the outflows. The estimated outflow energetics are consistent with the theoretical expectations for energy-conserving outflows from AGNs, yet we find no supporting evidence of instantaneous quenching of star formation due to the outflows., Comment: 25 pages, 27 figures, 5 tables; Accepted for publication in ApJ

Context. All globular clusters (GCs) studied in detail host two or more populations of stars (the multiple population phenomenon). Theoretical models suggest that the second population is formed from gas polluted by processed material produced by massive stars of the first generation. However the nature of the polluters is matter of strong debate. Several candidates have been proposed: massive main-sequence stars (fast rotating or binaries), intermediate-mass AGB stars, or SNeII. Aims: We studied red giant branch (RGB) stars in the GC M4 (NGC 6121) to measure their chemical signature. Our goal is to measure abundances for many key elements (from Li to Eu) in order to derive constraints on the polluters responsible for the multiple populations. Methods: We observed 23 RGB stars below the RGB-bump using the GIRAFFE spectroscopic facility installed on VLT2. Spectra cover a wide range and allowed us to measure light (Li, C, 12C/13C, N, O, Na, Mg, Al), alpha (Si, Ca, Ti), iron-peak (Cr, Fe, Ni), light-s (Y), heavy-s (Ba), and r (Eu) elements. We supplemented this study by analyzing an additional subsample of the UVES spectra in order to gather further clues about light s-elements of different atomic number (Y and Zr). Results: We confirm the presence of a bimodal population. Stars can be easily separated according to their N content. The two groups have different C, 12C/13C, N, O, Na content, but share the same Li, C+N+O, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Zr, Ba and Eu abundance. Quite surprisingly the two groups differ also in their Y abundance. This result is strongly supported also by the analysis of the UVES spectra. Conclusions: The absence of a spread in alpha-elements, Eu and Ba makes SNeII and AGB stars unlikely as polluters. On the other hand, massive main-sequence stars can explain the bimodality of Y through the weak s-process. This statement is confirmed independently also by literature data on Rb and Pb. The lack of a Mg/Al spread and the extension of the [O/Na] distribution suggest that the mass of the polluters is between 20 and 30 M&sun;. This implies a formation time scale for the cluster of 10 ÷ 30 Myr. This result is valid for M4. Other clusters such as NGC 1851, M 22, or omega Cen have different chemical signatures and may require other kinds of polluters. Based on observations made with ESO telescopes at La Silla Paranal Observatory under program ID 083.B-0083.Table 6 is available in electronic form at http://www.aanda.org

Broad, double-peaked, Balmer emission lines are found in the optical spectra of a relatively small fraction of active galactic nuclei. They can be an extremely useful diagnostic for the structure and dynamics of the “broad-line region” (the medium that emits the broad emission lines). In general terms the rarity and shapes of their profiles provide strong constraints on universal models of the broad-line region. A series of observational tests and basic physical considerations suggest that these lines are emitted from a flat, rotating disk, very likely the outer parts of the accretion disk that fuels the black hole. In the context of models for accretion disk winds, double-peaked emission lines originate in disks with feeble winds of low optical depth. Therefore, they provide evidence that the outer accretion disk and its associated wind are the source of the broad emission lines. Within this framework, double-peaked Balmer emission lines and corresponding high-ionization lines in the near-ultraviolet allow us to study the conditions under which the winds become dense and the onset of significant outflows. Moreover, double-peaked emission lines give us a direct view of the dense material of the disk proper and allow us to study dynamical perturbations and other transient behavior though the long-term variability of their profiles.

We present spectra of the nuclear regions of 50 nearby (D = 1–92 Mpc, median = 20 Mpc) galaxies of morphological types E to Sm. The spectra, obtained with the Gemini Near-IR Spectrograph on the Gemini North telescope, cover a wavelength range of approximately 0.85–2.5 μm at R ~ 1300–1800. There is evidence that most of the galaxies host an active galactic nucleus (AGN), but the range of AGN luminosities (log (L $_{2-10\;{\rm keV}}$ [erg s−1]) = 37.0–43.2) in the sample means that the spectra display a wide variety of features. Some nuclei, especially the Seyferts, exhibit a rich emission-line spectrum. Other objects, in particular the type 2 Low Ionization Nuclear Emission Region galaxies, show just a few, weak emission lines, allowing a detailed view of the underlying stellar population. These spectra display numerous absorption features sensitive to the stellar initial mass function, as well as molecular bands arising in cool stars, and many other atomic absorption lines. We compare the spectra of subsets of galaxies known to be characterized by intermediate-age and old stellar populations, and find clear differences in their absorption lines and continuum shapes. We also examine the effect of atmospheric water vapor on the signal-to-noise ratio achieved in regions between the conventional NIR atmospheric windows, which are of potential interest to those planning observations of redshifted emission lines or other features affected by telluric H2O. Further exploitation of this data set is in progress, and the reduced spectra and data reduction tools are made available to the community., C.R.A. is supported by a Marie Curie Intra European Fellowship within the 7th European Community Framework Programme (PIEF-GA-2012-327934). L.C.H. acknowledges support from the Kavli Foundation, Peking University, and the Chinese Academy of Science through grant No. XDB09030100 (Emergence of Cosmological Structures) from the Strategic Priority Research Program. A.A.-H. acknowledges support from the Spanish Plan Nacional de Astronomía y Astrofísica under grant AYA2012-31447. A.R.A. thanks the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for partial support of this work through grant 307403/2012-2.

et al., We analyse the stellar absorption features in high signal-to-noise ratio (S/N) near-infrared (NIR) spectra of the nuclear region of 12 nearby galaxies, mostly spirals. The features detected in some or all of the galaxies in this sample are the TiO (0.843 and 0.886 μm), VO (1.048 μm), CN (1.1 and 1.4 μm), H2O (1.4 and 1.9 μm) and CO (1.6 and 2.3 μm) bands. The C2 (1.17 and 1.76 μm) bands are generally weak or absent, although C2 (1.76 μm) may be weakly present in the mean galaxy spectrum. A deep feature near 0.93 μm, likely caused by CN, TiO and/or ZrO, is also detected in all objects. Fitting a combination of stellar spectra to the mean spectrum shows that the absorption features are produced by evolved stars: cool giants and supergiant stars in the early- or thermally pulsing asymptotic giant branch (E-AGB or TP-AGB) phases. The high luminosity of TP-AGB stars, and the appearance of VO and ZrO features in the data, suggest that TP-AGB stars dominate these spectral features. However, a contribution from other evolved stars is also likely. Comparison with evolutionary population synthesis models shows that models based on empirical libraries that predict relatively strong NIR features provide a more accurate description of the data. However, none of the models tested accurately reproduces all of the features observed in the spectra. To do so, the models will need to not only improve the treatment of TP-AGB stars, but also include good quality spectra of red giant and E-AGB stars. The uninterrupted wavelength coverage, high S/N and quantity of features we present here will provide a benchmark for the next generation of models aiming to explain and predict the NIR properties of galaxies., The Brazilian authors thank CNPq and FAPERGS support. LCH acknowledges support by the Chinese Academy of Science through grant no. XDB09030102 (Emergence of Cosmological Structures) from the Strategic Priority Research Program and by the National Natural Science Foundation of China through grant No. 11473002. CRA is supported by a Marie Curie Intra European Fellowship within the 7th European Community Framework Programme (PIEF-GA-2012-327934).

Using archival Chandra observations of 19 LINERs we explore the X-ray properties of their inner kiloparsec to determine the origin of their nuclear X-ray emission, to investigate the presence of an AGN, and to identify the power source of the optical emission lines. The relative numbers of LINER types in our sample are similar to those in optical spectroscopic surveys. We find that diffuse, thermal emission is very common and is concentrated within the central few hundred parsec. The average spectra of the hot gas in spirals and ellipticals are very similar to those of normal galaxies. They can be fitted with a thermal plasma (kT~0.5 keV) plus a power law (photon index of 1.3-1.5) model. There are on average 3 detected point sources in their inner kiloparsec with L(0.5-10 keV)~10^37-10^40 erg/s. The average cumulative luminosity functions for sources in spirals and ellipticals are identical to those of normal galaxies. In the innermost circle of 2.5" radius in each galaxy we find an AGN in 12 of the 19 galaxies. The AGNs contribute a median of 60% of the 0.5-10 keV luminosity of the central 2.5" region, they have luminosities of 10^37-10^39 erg/s (Eddington ratios 10^-8 to 10^-5). The ionizing luminosity of the AGNs is not enough to power the observed optical emission lines in this particular sample. Thus, we suggest that the lines are powered either by the mechanical interaction of an AGN jet (or wind) with the circumnuclear gas, or by stellar processes, e.g. photoionization by post-AGB stars or young stars., Accepted by Ap.J. 23 pages, 8 figures, emulatepj format, images of fig 1 not included, for complete PDF preprint see http://www.astro.psu.edu/users/mce/preprints/

et al., We examine the stellar velocity dispersions (σ) of a sample of 48 galaxies, 35 of which are spirals, from the Palomar nearby galaxy survey. It is known that for ultra-luminous infrared galaxies (ULIRGs) and merger remnants, the σ derived from the near-infrared CO band heads is smaller than that measured from optical lines, while no discrepancy between these measurements is found for early-type galaxies. No such studies are available for spiral galaxies – the subject of this paper. We used cross-dispersed spectroscopic data obtained with the Gemini Near-Infrared Spectrograph, with spectral coverage from 0.85 to 2.5 μm, to obtain σ measurements from the 2.29 μm CO band heads (σCO) and the 0.85 μm calcium triplet (σCaT). For the spiral galaxies in the sample, we found that σCO is smaller than σCaT, with a mean fractional difference of 14.3 per cent. The best fit to the data is given by σopt = (46.0 ± 18.1) + (0.85 ± 0.12)σCO. This ‘σ-discrepancy’ may be related to the presence of warm dust, as suggested by a slight correlation between the discrepancy and the infrared luminosity. This is consistent with studies that have found no σ-discrepancy in dust-poor early-type galaxies, and a much larger discrepancy in dusty merger remnants and ULIRGs. That σCO is lower than σopt may also indicate the presence of a dynamically cold stellar population component. This would agree with the spatial correspondence between low-σCO and young/intermediate-age stellar populations that has been observed in spatially resolved spectroscopy of a handful of galaxies., RAR acknowledges support from FAPERGS (project no. 12/1209-6) and CNPq (project no. 470090/2013-8). LCH acknowledges support from the Kavli Foundation, Peking University, and grant no. XDB09030102 (Emergence of Cosmological Structures) from the Strategic Priority Research Program of the Chinese Academy of Sciences. ARA acknowledges CNPq for partial support to this work through grant 307403/2012-2. LM thanks CNPq through grant 305291/2012-2. LC acknowledges support from the Special Visiting Researcher Fellowship (PVE 313945/2013-6) under the Brazilian Scientific Mobility Program ‘Ciencias sem Fronteiras’. RR acknowledges funding from FAPERGs (ARD 11/1758-5) and CNPq (PeP 304796/2011-5). CRA is supported by a Marie Curie Intra European Fellowship within the 7th European Community Framework Programme (PIEF-GA-2012-327934) and by the Spanish Ministry of Science and Innovation (MICINN) through project PN AYA2010-21887-C04.04.

We present a Chandra, Suzaku and Rosat study of the hot Intra Group Medium (IGrM) of the relaxed fossil group/ poor cluster RXJ1159+5531. This group exhibits an advantageous combination of flat surface brightness profile, high luminosity and optimal distance, allowing the gas to be detected out to the virial radius (Rvir=R108=1100 kpc) in a single Suzaku pointing, while the complementary Chandra data reveal a round morphology and relaxed IGrM image down to kpc scales. We measure the IGrM entropy profile over 3 orders of magnitude in radius, including 3 data bins beyond 0.5R200 with azimuthal coverage (>30%). We find no evidence that the profile flattens at large scales (>R500), and when corrected for the enclosed gas fraction, the entropy profile is very close to the predictions from self-similar structure formation simulations, as seen in massive clusters. Within Rvir, we measure a baryon fraction of 0.17+/-0.02, consistent with the Cosmological value. These results are in sharp contrast to the gas behaviour at large scales recently reported in the Virgo and Perseus clusters, and indicate that substantial gas clumping cannot be ubiquitous near Rvir, at least in highly evolved (fossil) groups., 22 pages, 17 figures. Minor modifications; results and conclusions unaffected. Accepted for publication in The Astrophysical Journal

We present a compilation of spectral energy distributions of 35 weak AGNs in LINERs using recent data from the published literature. We make use of previously published compilations of data, after complementing and extending them with more recent data. The main improvement in the recent data is afforded by high-spatial resolution observations with the Chandra X-Ray Observatory and high-spatial resolution radio observations utilizing a number of facilities. In addition, a considerable number of objects have been observed with the HST in the near-IR through near-UV bands since the earlier compilations were published. The data include upper limits resulting from either non-detections or observations at low spatial resolution that do not isolate the AGN. For the sake of completeness, we also compute and present a number of quantities from the data, such as alpha-ox, bolometric corrections, bolometric luminosities, Eddington ratios, and the average SED. We anticipate that these data will be useful for a number of applications. In a companion paper, we use a subset of these data ourselves to assess the energy budgets of LINERs., emulateapj format, 12 pages in total, to appear in ApJS, one large table and one large figure abridged (will be available in electronic journal)

Using the SEDs of the weak AGNs 35 LINERs presented in a companion paper, we assess whether photoionization by the weak AGN can power the emission-line luminosities measured through the large (few-arcsecond) apertures used in ground-based spectroscopic surveys. Spectra taken through such apertures are used to define LINERs as a class and constrain non-stellar photoionization models for LINERs. Therefore, our energy budget test is a self-consistency check of the idea that the observed emission lines are powered by an AGN. We determine the ionizing luminosities and photon rates by integrating the observed SEDs and by scaling a template SED. Even if all ionizing photons are absorbed by the line-emitting gas, more than half of our LINERs suffer from a deficit of ionizing photons. In 1/3 of LINERs the deficit is severe. If only 10% of the ionizing photons are absorbed by the gas, there is an ionizing photon deficit in 85% of LINERs. We disfavor the possibility that additional electromagnetic power, either obscured or emitted in the unobservable far-UV band, is available from the AGN. We consider other power sources such as mechanical heating by compact jets and photoionization by young or old stars. Photoionization by young stars may be important in a small fraction of cases. Mechanical heating provides enough power in most cases but it is not clear how this power is transferred to the emission-line gas. Photoionization by post-AGB stars is an important power source; it provides more ionizing photons that the AGN in more than half of the LINERs and enough ionizing photons to power the emission lines in 1/3 of the LINERs. It appears likely that the emission-line spectra of LINERs obtained from the ground include the sum of emission from different regions where different power sources dominate., Comment: emulateapj format, 12 pages in total, to appear in ApJ

In an effort to explain the short-timescale variability of the broad, double-peaked profiles of some active galactic nuclei, we constructed stochastically perturbed accretion disk models and calculated H alpha line profile series as the bright spots rotate, shear and decay. We determined the dependence of the properties of the line profile variability on the spot properties. We compared the variability of the line profile from the models to the observed variability of the H alpha line of Arp 102B and 3C 390.3. We find that spots need to be concentrated in the outer parts of the line emitting region to reproduce the observed variability properties for Arp 102B. This rules out spot production by star/disk collisions and favors a scenario where the radius of marginal self-gravity is within the line emitting region, creating a sharp increase in the radial spot distribution in the outer parts. In the case of 3C 390.3, all the families of models that we tested can reproduce the observed variability for a suitable choice of model parameters., 27 pages, 8 figures, accepted for publication in ApJ

We have obtained observations of the ultraviolet spectrum of AM CVn, an ultra-short-period helium cataclysmic variable, using the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope (HST). We obtained data in time-tag mode during two consecutive orbits of HST, covering 1600-3150 and 1140-1710 Angstrom, respectively. The mean spectrum is approximately flat in f-nu. The absorption profiles of the strong lines of N V, Si IV, C IV, He II, and N IV are blue-shifted and in some cases asymmetric, evidencing a wind that is partly occulted by the accretion disk. There is weak red-shifted emission from N V and He II. The profiles of these lines vary mildly with time. The light curve shows a decline of ~20% over the span of the observations. There is also flickering and a 27 s (or 54 s) "dwarf nova oscillation", revealed in a power-spectrum analysis. The amplitude of this oscillation is larger at shorter wavelengths. We assemble and illustrate the spectral energy distribution (s.e.d.) of AM CVn from the ultraviolet to the near-infrared. Modeling the accretion phenomenon in this binary system can in principle lead to a robust estimate of the mass accretion rate on to the central white dwarf, which is of great interest in characterizing the evolutionary history of the binary system. Inferences about the mass accretion rate depend strongly on the local radiative properties of the disk, as we illustrate. Uncertainty in the distance of AM CVn and other parameters of the binary system presently limit the ability to confidently infer the mass accretion rate., Accepted by the Astronomical Journal

We summarise the properties of selected supernova remnants (SNRs) which have elongated envelopes that could house relativistic jets. We present MOPRA and SEST millimeter observations of these objects, showing correlation between known X-ray hot spots and molecular cloud density as signified by the detection of a CO(1-0) line flux.

We have used Chandra archival observations of 19 galaxies hosting LINERs to explore the morphology and source population of their inner kiloparsec. Our goal was, in general, to determine the power source behind their nuclear X-ray emission and, in particular, to investigate the presence of an AGN. We find an AGN in 12 of the 19 galaxies in the sample. We also find that diffuse, thermal emission is common with properties very similar to what is found in normal galaxies. In 10 out of the 19 galaxies, the diffuce emission dominates the nuclear X-ray power. The X-ray point-source populations were studied by producing cumulative luminosity functions and their properties are also similar to what is found in normal galaxies.

We explore the connection between active galactic nuclei (AGNs) with single- and double-peaked broad Balmer emission lines by using models dealing with radiative transfer effects through a disk wind. Our primary goal is to assess the applicability of the Murray and Chiang model by making an extensive and systematic comparison of the model predictions with data. In the process, we also verify the original derivation and evaluate the importance of general relativistic effects. As the optical depth through the emission layer increases, the peaks of a double-peaked profile move closer and eventually merge, producing a single peak. The properties of the emission line profile depend as sensitively on the geometric parameters of the line-emitting portion of the disk as they do on the disk-wind parameters. Using a parameter range that encompasses the expected characteristics of the broad-line regions in AGNs, we construct a database of model profiles and measure a set of diagnostic properties. Comparisons of the model profiles with emission lines from a subset of Sloan digital Sky Survey quasars show that observed lines are consistent with moderately large optical depth in the disk wind and a range of disk inclinations i {approx}< 45 Degree-Sign . Including relativistic effectsmore » is necessary to produce the asymmetries of observed line profiles.« less