RPS in Galaxy Clusters Analysis

RPS in Galaxy Clusters Analysis Jellyfish:  A  spectroscopic  study  of  ram-pressure  stripping  in  massive  galaxy  clusters* ABSTRACT We continue our exploration of ram-pressure stripping (RPS) in massive galaxy clusters at z>0.3 by assessing the spectroscopic properties of RPS candidates selected previously based on their morphological appearance in Hubble Space Telescope images. We confirm cluster membership for 55 of our candidates, thereby tripling the number of RPS candidates known at z>0.2. Although many of these systems are too faint and too distant for the kind of in-depth investigation required to unambiguously confirm or refute the presence of RPS, the ensemble properties of our sample are consistent with increased star formation, and many of the selected galaxies exhibit visible debris trails. Specifically, about two thirds of all galaxies exhibit line emission ([OII]ÃŽÂ »3727AËÅ ¡ , HÃŽÂ ², and, where observationally accessible, HÃŽÂ ±) consistent with ro- bust star-formation rates that significantly exceed those expected for systems on the galaxy main sequence. We find no significant depe ndence of either the presence of line emission or the inferred star-formation rate on the relaxation state of the host cluster. Although we caution that our sample may contain not only galaxies undergoing RPS by the diffuse intra-cluster medium (ICM), but also minor mergers located at the low-density cluster outskirts and merely projected onto the cluster cores, we expect our results to facilitate and inform realistic process models of the stripping process by providing the first statistically significant sample of RPS candidates in truly massive clusters. While extremely rapid removal of the intrastellar medium is not ruled out by our findings, extended periods of triggered star formation are clearly an integral component of the physics of ICM-galaxy interaction in massive clusters. INTRODUCTION Spiral and elliptical galaxies are both commonly observed in the universe but inhabit (and dominate) very different environments. The inverse correlation between spiral fraction and density of the environment has long been established based on both galaxy mor- phology and colour (Dressler 1980; Baldry et al. 2006) and is so pronounced as to suggest causation. Since the preponderance of red, elliptical galaxies is not limited to the densest environments (i.e., the cores of massive galaxy clusters) but is notable already in groups of galaxies (Blanton Moustakas 2009), several phys- ical mechanisms may be responsible for the observed segregation of galaxy types and appear to be have been at work for several Gyr, as evinced by the steady increase in the dominance of ellipticals in  clusters from zà ¢Ã‹â€ Ã‚ ¼1.5 to the present day (Scoville et al. 2013). * Most of the data presented herein were obtained at the W.M. Keck Ob- servatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aero- nautics and Space Administration. The observatory was made possible by the generous finical support of the W.M. Keck Foundation. Although simulations have indicated that elliptical galaxies can form directly through spherical collapse of dark-matter halos in high-density environments (e.g. Navarro Benz 1991), it is widely accepted that transformations of galaxies from late to early types are central to the creation of the Hubble sequence. These occur in a range of environments and, most likely, over a range of character- istic timescales. While slow-acting gradual effects such as galaxy harassment (Moore et al. 1996, 1998) are bound to contribute, more violent interactions have been shown to be highly effective in turning disk galaxies into spheroids. In modestly dense environ- ments with commensurately modest relative galaxy velocities, i.e., in galaxy groups and at the outskirts of more massive galaxy clus- ters, galaxy mergers as predicted by Holmberg (1941) and explored in numerical simulations (e.g., Toomre Toomre 1972; Barnes Hernquist 1992, 1996; Mihos Hernquist 1996) can create a wide range of remn ants, including spheroidal galaxies (Toomre 1977; Hammer et al. 2009). By contrast, at the extreme opposite end of the density range where galaxies move too fast to have a signif- icant cross section for merging, ram-pressure stripping (RPS) by the diffuse intra-cluster medium (ICM) has been predicted (Gunn   Gott 1972), simulated (e.g., Farouki Shapiro 1980; Vollmer et   al. 2001; Roediger Hensler 2005; Domainko et al. 2006; Kron- berger et al. 2008; Bekki 2009; Tonnesen Bryan 2010), and ob- served across a wide range of wavelengths. Numerous studies have established that RPS is capable of rapidly displacing and removing gas from spirals falling into galaxy clusters (e.g., White et al. 1991; Rangarajan et al. 1995; Veilleux et al. 1999; Vollmer et al. 2008; Sun et al. 2010). We here present new results from an observational study de- signed to identify and characterise RPS events in massive clusters at intermediate redshift. Our project is motivated by the fact that, while RPS has been well studied in the local Universe (e.g., Sun et al. 2006; Sun, Donahue Voit 2007; Merluzzi et al. 2013; Fuma- galli et al. 2014; Poggianti et al. 2016), work at higher redshift has advanced more slowly, due to the obvious challenges in attaining commensurate signal and spatial resolution (but see Poggianti et al. 2004; Cortese et al. 2007; Moran et al. 2007; Owers et al. 2012). It is only at z>0.2, however, that the volume probed by any clus- ter survey becomes large enough to contain a significant number of truly massive clusters (systems more massive than Coma), i.e., clusters that allow us to study RPS over the full range of environ- ments, from the only mildly overdense cluster outskirts to extreme densities in the core regions that are never reached in local cluster s like Virgo. In this paper we examine the spectroscopic properties of galaxies tentatively identified as undergoing RPS in massive galaxy clusters at z>0.3. All clusters considered for this work were iden- tified by their X-ray emission and optically confirmed in the course of the Massive Cluster Survey (MACS; Ebeling et al. 2001, 2007, 2010; Mann Ebeling 2012). Potential stripping events were se- lected based on the morphology of galaxies in images of MACS cluster cores obtained with the Advanced Camera for Surveys (ACS) aboard the Hubble Space Telescope (HST) (see Repp Ebeling, in preparation, for an overview of this dataset). In Ebel- ing et al. (2014, hereafter E14) we presented a first sample of six textbook cases of RPS identified visually in these data and, ow- ing to their appearance, referred to as jellyfish (Fig. 1). Our sec- ond paper (McPartland et al. 2016, hereafter M16) defined a cus- tomized set of morphological selection criteria used to compile a larger sample of 223 potential RPS candidates and examined the spatial distribution and apparent projected direction of motion of the most plausible candidates. In this third paper, we present, dis- cuss, and interpret the results of extensive spectroscopic follow-up observations of the M16 sample. Our paper is organised as follows: After a brief introduction in  §1,  §2 describes the setup and execution of our spectroscopic  follow-up observations of RPS candidates, the data reduction, as well as our criteria to assess cluster membership for any given  galaxy. In  §3 we derive fundamental spectral properties of the con-firmed cluster members, infer star-formation rates, and estimate their stellar mass.  §4 compares the properties of RPS candidates  with those of the general population of star-forming galaxies, dis- cusses physical triggering mechanisms, and investigates correla- tions between the star-formation rate of RPS candidates and the relaxation state of the host cluster. We summarise our findings in  Ãƒâ€šÃ‚ §5. Throughout this paper we adopt the concordance ΆºCDM cos-mology, characterised by à ¢Ã¢â‚¬Å¾Ã‚ ¦m= 0.3, à ¢Ã¢â‚¬Å¾Ã‚ ¦ÃƒÅ½Ã¢â‚¬ º = 0.7, and H0 = 70 km sà ¢Ã‹â€ Ã¢â‚¬â„¢1 Mpcà ¢Ã‹â€ Ã¢â‚¬â„¢1. Figure1.HST/ACS snapshot image of MACSJ0451-JFG1, a textbook case of ram-pressure stripping from the E14 sample. The red and yellow arrows mark the inferred direction of motion in the plane of the sky and the di- rection to the cluster centre, respectively. Note that the tell-tale jellyfish morphology of this z=0.43 galaxy is readily discernible only thanks to the superb resolution of HST/ACS. (Reproduced from E14) SPECTROSCOPIC OBSERVATIONS AND DATA REDUCTION The targets of our spectroscopic follow-up observations were drawn from the set of 223 galaxies tentatively identified by M16 as undergoing ram-pressure stripping. We refer to M16 for a detailed discussion of the morphological criteria applied to select these can- didates from a master catalogue of over 15,000 galaxies detected in short HST/ACS exposures in the F606W and F814W bands of 63 MACS clusters in the redshift range of 0.30.7. A comprehen- sive description of the HST observations used by M16 is provided by Repp Ebeling (in preparation). Since most of the RPS candidates from the list of 223 were targeted by us in spectroscopic observations of MACS clusters that supported several complementary research projects, compromises had to be made in the design of the observations. In order to max- imise scientific returns, clusters that feature large numbers of tar- gets for each of the different projects were given priority, resulting in a bias in favour of clusters with multiple RPS candidates. In ad- dition, the simultaneous focus on many targets made it impossible to optimise the orientation of individual slits or even the position angle of the entire mask for the study of RPS candidates. Keck/DEIMOS observations All spectroscopic data for this work were obtained with the Deep Imaging Multi-Object Spectrograph (DEIMOS; Faber et al. 2003) on the Keck II 10m telescope on Maunakea. All multi-object spec- troscopy (MOS) masks used 1//-wide slits of at least 8//length, i.e., long enough to allow sky subtraction from in-slit data. Spectra were obtained using the 600 l/mm Zerodur grating set to a central wavelength of 6300AËÅ ¡ ; the GG455 blocking filter was employed to prevent second-order contamination at ÃŽÂ »>9000AËÅ ¡ . Exposure times  ranged from 3ÃÆ'-600 to 3ÃÆ'-1200 seconds. The seeing during these  observations was typically 0.8//. All data were reduced with the DEIMOS DEEP2 pipeline (Cooper et al. 2012; Newman et al. 2013), creating sky-subtracted and wavelength-calibrated one- and two-dimensional spectra. Redshifts were determined from the one- dimensional spectra using elements of the SpecPro software pack- age (Masters Capak 2011). Overall 110 RPS candidates were observed in 26 MACS clus-ters. Cluster membership We establish (likely) cluster membership by comparing the differ- ence between an RPS candidates redshift and the systemic redshift of the cluster with the cluster velocity dispersion. The latter is com- puted from all galaxy redshifts measured for the respective cluster in the course of the extensive spectroscopic follow-up work per- formed by the MACS team; a description of the underlying data and of the procedure employed to determine robust velocity dispersions for MACS clusters is provided by Repp Ebeling (in preparation). Although it is possible that some of the galaxies for which we rule out cluster membership are in fact still undergoing RPS within their local environment in the fore- or background of the respective MACS cluster, the majority of such non-cluster members are more likely to owe their disturbed optical morphology (and thus their selection in M16) to merger events or to gravitational lensing. In the following, we thus limit the term RPS candidates to galaxies classified as likely cluster members based on their radial velocity within the comoving cluster rest frame. Spectral corrections and flux calibration The reduced spectra created with the DEEP2 pipeline are wave- length-calibrated and thus allow redshift measurements that are ac- curate to within the limits set by the instrumental setup and the pre- cision of the dispersion solution. The determination of line fluxes and, in particular, line-flux ratios across a significant wavelength range, however, require flux-calibrated spectra. In addition, flux lost during the data-reduction process (due to CCD defects, non- optimal definition of spectral apertures, and, importantly, the finite slit width) needs to be recovered, if the measured line fluxes are to be interpreted as characteristics of the observed galaxy as a whole. Whereas corrections for missing flux are fairly straightforward to apply, flux calibration is notoriously difficult for multi-object spec- trographs (especially when the respective observations were not performed at the parallactic angle), owing to spatial variations in the instrument response across the field of vie w covered by the slit mask. Before flux calibration is performed, we visually inspect the two-dimensional spectra of all RPS candidates classified as likely cluster members. We manually mask out the spectral traces of non- target sources falling serendipitously into a slit, fill in bad detector columns, and re-extract the target spectra within an aperture that maximizes the object flux at all wavelengths. We then resort to external means to calibrate these spectra by tying the latter at two wavelengths to the photometry obtained for the respective galaxy with HST/ACS in the F606W and F814W passbands. To this end, we convolve the HST images in these two filters with a Gaussian whose full width at half maximum is matched to the average seeing during our DEIMOS observations and then integrate the flux within the DEIMOS slit (Fig. 2). The re- sulting linear calibration, illustrated in Fig. 3, achieves two goals: it Figure2.Example of the procedure applied to obtain accurate absolute photometry for the flux entering a slit on our MOS masks. Left: HST/ACS image of an RPS candidate in the F606W filter; overlaid are isophotal flux contours (green) and the slit as positioned during the DEIMOS observation. Right: As left, but convolved with a Gaussian kernel that mimics the seeing of the groundbased observation and rotated to align the slit with the image axes. 80 3000 250060 2000 40 1500 1000 20 500 00 40005000600070008000900010000 wavelength (A) Figure 3.DEIMOS spectrum of one of our RPS candidates before and af- ter flux calibration and slit size correction. The green and red lines show the throughput (in arbitrary units) of the ACS/F606W and F814W filters, respectively, used to anchor the flux calibration. (1) crudely corrects for wavelength-dependent variations in the to- tal throughput of our observational setup; and (2) extrapolates the spectrum actually observed through the slit to the spectrum of the entire galaxy. Note that the validity of the latter correction rests on the implicit assumption that the spectrum recorded within the slit is representative of that of the galaxy as a whole. Although this as- sumption is not necessarily well justified, it is widely applied and ensures consistency and comparability between line fluxes (and de- rived properties like star-formation rates) obtained in studies using different instrumental setups and observational strategies. PHYSICAL PROPERTIES OF RPS CANDIDATES Stellar mass In order to establish the locus of our RPS candidates within the general population of star-forming galaxies, we need to ensure that comparisons are made only between galaxies of comparable stellar mass. While the stellar mass of galaxies in our sample cannot re- liably be determined from only the HST/ACS data in the F606W  and F814W used for their original selection by M16, or from the optical spectroscopy within the à ¢Ã‹â€ Ã‚ ¼5000 à ¢Ã‹â€ Ã¢â‚¬â„¢9000AËÅ ¡ range described in Section 2, photometry across a wider spectral range that extends into the near-infrared (NIR) regime is well suited to constrain the spectral-energy distribution (SED) of galaxies and thus their stel- lar masses. For a significant fraction (QUANTIFY) of our cluster fields, the required data are available thanks to imaging observa- tions of MACS clusters with the NIR channel of HSTs Wide-Field Camera 3 (WFC3) performed for the CLASH project (Postman et al. 2012) and the MACS SNAPshot programs GO-12188 and -12884 (PI: Ebeling) described in Repp Ebeling (in preparation). The resulting photometry in the XXX passbands (CLASH) for 15 of our RPS candidates, and in the F606W, F814W, F110W, and F140W filters (SNAPshot programs) for an additional 17 galaxies, is fit with synthetic spectral templates using LePhare (Arnouts et al. 1999; Ilbert et al. 2006), an SED modeling code developed pri- marily for the determination of photometric redshifts of galaxies in the COSMOS field. Emission-line fluxes and star-formation rates 3.2.1   Extinctioncorrection DISCUSSION BPT diagram RPS candidates and the galaxy main sequence Properties of the host clusters CONCLUSIONS ACKNOWLEDGEMENTS We thank Elke Roediger for helpful discussions on the latest in nu- merical simulations of ram-pressure stripping and how to further constrain them via imaging and spectroscopic observations. Most of the data presented herein were obtained at the W. M. Keck Ob- servatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The observa- tory was made possible by the generous finical support of the W. 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Learning a Second Language

Learning a second language after using your native language all your life can truly frustrating and overwhelming at first. But as one begins to chip away at the language and begin to some understand words, these form a foundation or scaffold upon which you can understand more words, primarily in context. More words, more context and this then creates cycle that helps towards achieving fluency in the target or second language. Mei-Yu (1998) once said that in the acquisition of oral language, â€Å"young children are active agents†, constantly process the language inputs that they are constantly exposed to and define and refine them ways that makes sense to them on a personal level. Children create hypotheses or theories about language rules, constantly filtering these theories through active engagement or connections with the more competent language users in their immediate environment. Unconsciously, they learn to recognize contexts and begin acquiring fine discrimination in their use of a language. This means that for a second language learner, the best way to learn is through immersion in the language. Total immersion creates a â€Å"sink or swim† instinct within the individual. The need to communicate and express one’s self will supersede all barriers to learning, and the individual will learn the language because of the instinctive need to survive. Children are especially natural linguists, able to effortlessly discern language rules and allow then to learn as many languages as they are exposed to. (Alyousef, 2005) However, the older we get, these natural language processes are replaced by conscious awareness of rules, which hinders the learning of a new language. For adults, the process of learning through immersion may take longer than for adults, but the process of second language acquisition remains essentially the same, especially if there is total immersion in the target language. For individuals moving to a new land permanently, total immersion will not be a problem. The â€Å"sink or swim† concept is so very true in the learning of a second language, the language must be learned in order to survive in society, then it most certainly be learned, it will only be a matter of time. Indeed learning a new language is all about exposure, but in most cases, such is not possible. For most of us, we learn a second language through formal and conscious lessons in second language classes. For people who are learning a new language, the best way to do so is through a strategy. For adult learners, it is important to follow some guidelines in order to facilitate language learning. The first step would be is to make an honest assessment of your competencies in the target language; do you have some basic knowledge or none at all? The second step is to analyze the language being taught and recognize similarities between the two. Teachers should be the one to initiate this. Language teachers should recognize individual skills and competencies which can be used to scaffold the new concepts being learned.   Building upon prior knowledge or what one already knows or is already skilled at is the best way to learn something new. In terms of language learning, the important thing is to reinforce the prior knowledge and connect it with the target skill, regardless of the languages involved. Starting with what you know is the best way to attack second language learning. When an individual approaches a lesson armed with knowledge and skills they already have, they have more confidence in exploring the new language. It is also encouraging because it gives you a sense of success and accomplishment early on in the lesson, something which is very important to maintain student motivation. Following similarities and prior knowledge, then learning can shift to the differences in the two languages involved to allow them to distinguish one from the other. Using prior knowledge once again, the learners should be allowed to recognize these differences themselves.   (Alyousef, 2005, p.7) Prior knowledge is a learning strategy that second language learners must use so that they will not feel so powerless while learning a new language. For those learning a second language, it is also important for the individual to realize why they need to learn the target language. Motivation is a crucial element of learning; if the target language must be learned to make an individual functional in society, then this need will facilitate the learning. (Crystal, 1987) Once the similarities have been established and the differences distinguished between the two alphabets, then the next is to focus on reinforcing the target language’s alphabet system and how their sounds are produced, making occasional references to the alphabet of the native language. These references will reinforce the connections between the two languages and help the student in the learning process. This strategy is meant to make the third-grade students be comfortable with the target alphabet by relating them to their native alphabet. Eventually, such references to the native alphabet will be gradually eliminated. This way the students can be fluent in the second alphabet independent of the mother tongue. (Mora, 2002) Of course for people who have achieved a certain level of fluency in the target language, the next step is to improve pronunciation. Knowing how to speak in a second language will not be of much value if you cannot be understood because of how you say it. Pronunciation can be a barrier in communication, so being able to say words correctly is crucial. The good thing is that accent is very easy to neutralize. Speech production is universal and the mechanism is the same for all of us. As such, we can learn to produce old sounds in new ways, such as when we attempt to pronounce a word differently. (Mora, 2002) But it must also be said that training the tongue to say words in new ways takes discipline. It can also be frustrating at first, and success can only be achieved with constant practice and conscious effort. This conscious production is necessary so that we can train the articulators to change its speech production habits. After knowing how the target sound is produced, the key is to constantly apply it until the body remembers it on its own without any conscious control on our part. Initially feedback is necessary; we need to listen to how we make the sounds so that we can make the mechanical adaptations necessary to achieve the change. To address this, we can record ourselves and monitor our progress as we continue to practice. Hearing how we improve over time is inspiring and encouraging. After all is said and done, there is great satisfaction in not just being fluent in a second language, but also being able to say it properly and clearly. Indeed, when it comes to learning a new language, the best way to do so is through patience and constant practice. If total immersion in the language is not possible, the best way is to form a strategy when approaching a language learning task. Whenever possible, the target language must be used so that the mind gets used to the language and begins to form a schema about it. References Alyousef, H. (2005). Teaching Reading Comprehension to ESL/EFL teachers. The Reading Matrix. Vol. 5, No. 2. Crystal, D. (1987). The Cambridge Encyclopedia of Language.   Cambridge University Press. Cambridge. Lu, Mei-Yu. (1998). Language Learning in Social and Cultural Contexts. ERIC Digest.   

A Funny Incident Essay

Hostel life is not without its disadvantages. The rich students get sufficient money from their parents and therefore spend lavishly. The poor boarders also urge their parents to increase their monthly allowance and spend their hard earned money on luxuries. The company of the rich also makes them pick up their bad habits. They start smoking. Some of them take to intoxicants and thereby ruin themselves. Another great defect in hostel life is the mismanagement on the part of the warden. The food supplied is simply unworthy of consumption by the students. The result in most cases is that in spite of the congenial atmosphere, they lose in health; they begin to hate the food supplied. In contrast to this is the life at home. The atmosphere at home, the love of parents, the affection bestowed on them by their brothers and sisters, the food they are supplied — all make them grow up into bright young boys and girls. A casual survey of the life of hostelers reveals the fact that most of the students who get into a merit list are those who have lived at home and not in hostels. The fact is that a boarder has limited time at his disposal for studies because of the rigid control; there are games and limited hours of study. The turning off of light at the time when they would like to study is a stumbling block in their way. When we examine the advantages and disadvantages of life in the hostel, we are convinced the home life is the best for the students

Corporate Social Responsibility In Business Free Essay Example, 3500 words

The green movement has given precedence to corporate social responsibility which has become the buzzword in the business world. To address the environmental needs and to meet the restrictions placed by the International agencies, strategy managers and high-level executives are incorporating various CSR initiatives. They opt to use PESTEL (Political, Economic, Social, Technological, Environmental and Legal) model to incorporate these initiatives by identifying which areas will be impacted by various CSR initiatives. For example, recycling of paper will address the political aspect of the PESTEL model as it is following the restrictions placed by the UN. With the help of this model, business-strategic managers can identify various CSR initiatives and adopt those addressing each aspect of the model at various strategic levels. Strategy defined as the direction and scope of an organization over the long-term: which achieves advantage for the organization through its configuration of re sources within a challenging environment, to meet the needs of markets and to fulfill stakeholder expectations (Johnson and Scholes 2006). From big to small organizations, the strategy is important as it highlights the direction the business is trying to take, the scope of their business, the expectation from their stakeholders, the utilization of their resources, and their advantages over its competitors. We will write a custom essay sample on Corporate Social Responsibility In Business or any topic specifically for you Only $17.96 $11.86/pageorder now In big organizations, strategy exists at several levels: corporate strategy, business unit strategy and functional unit strategy whereas in a small organization, the levels are intermingled with each other. The corporate strategy is concerned with the overall purpose and scope of the business (Mintzberg et al 2005). For example, Microsoft takes a strategic approach to accessibility in product planning, research and development, product development and testing. They are continuously working to make the computer easier to use and handle by building various accessibility features into Microsoft products.