Галактический Зоопарк

Why is galaxy morphology important?

To first order, the morphology of a galaxy is a tracer of the orbital dynamics of the stars in it, but it also carries an imprint of the processes driving star formation and nuclear activity in galaxies. Visual morphology produces classifications which are strongly correlated with other, physical parameters. To give a single example, the presence of multiple nuclei and extended tidal features indicates that the dominant mechanism driving star formation is an ongoing merger. Equally, the absence of such features implies that the evolution of the galaxy may be being driven by slower ('secular') processes.

Traditionally morphology has been derived either by visual inspection of galaxy images (e.g. Hubble 1926, de Vaucouleurs 1991, and more recently e.g. Nair and Abraham 2010 or via morphological parameters, such as Concentration, Asymmetry, Clumpiness, M20, the Gini coefficient, etc (e.g. Conselice 2003, Lotz et al. 2008). Strictly speaking, these parameters are morphological 'proxies', each with its own attendant biases, which are typically checked and calibrated against visual inspection. A visual approach is generally more resistant to changing signal-to-noise and resolution in images (e.g. Lisker 2008), making it an ideal method for determining galaxy morphology. Nevertheless, morphological parameters have been valuable for classifying large survey-scale datasets, for which visual inspection by individuals (or small groups of researchers) can be prohibitively time-consuming.

How did Galaxy Zoo Start?

Galaxy Zoo (Lintott et al. 2008, 2011) orginaly launched in July 2007, pioneering a novel method for performing large-scale visual classifications of survey datasets. Working with more than half a million members of the general public, the first phase of the project classified – via direct visual inspection - the entire Sloan Digital Sky Survey spectroscopic sample (around 1 million galaxies in total). With more than 40 classifications per object, Galaxy Zoo provided both a visual classification and an associated uncertainty (which is challenging to estimate if there are only a few human classifiers). The classifications themselves have been demonstrated to be of comparable accuracy to those derived by expert astronomers (see Lintott et al. 2008).

What are some Science Highlights from Galaxy Zoo?

The Galaxy Zoo science programme has contributed to a diverse set of topics, largely focused on the nearby and intermediate-redshift Universe. Some recent examples include the largest studies of galaxy mergers (Darg et al. 2010), tidal dwarf galaxies (Kaviraj et al. 2012), dust lanes in early-type galaxies (Kaviraj et al. 2012) and bars in disc galaxies (Masters et al. 2011, 2012) in the nearby Universe to date. One of the unique aspects of Galaxy Zoo over automated morphological measurements is the possibility of serendipitous discoveries (often aided by volunteer led discussion on the Galaxy Zoo Forum). These have included the discovery of 'green peas' (a class of compact extremely star-forming galaxies in the local Universe; Cardamone et al. 2009) and perhaps most famously "Hanny's Voorwerp" (Lintott et al. 2009) along with a survey of similar AGN-ionised gas clouds (Keel et al. 2012). The availability of a large sample of galaxies with both color and morphological information has led to the important realisation that color, not morphology, is most strongly correlated with environment (Bamford et al. 2009; Skibba et al. 2009), leading to intriguing subclasses of galaxies like red spiral galaxies (Masters et al. 2010) and blue ellipticals (Schawinski et al. 2009).

Why have there been so many phases of Galaxy Zoo?

The purpose of the Galaxy Zoo project is to answer a variety of scientific questions, to prepare the ground for morphological work using future instruments, and to produce samples of morphologically selected high-redshift galaxies for follow-up using instruments like the extremely large telescopes and ALMA. Galaxy Zoo launched with one specific survey, but has become a technique for analysis of galaxy images from any facility.

Over the years since we launched in 2007, Galaxy Zoo has made use of images from a variety of different telescopes, including SDSS, HST, Euclid, JWST, UKIRT, VST and the CTIO 4-m Blanco telescope. We have a summary of most of the different sets of images we have used in the Results Page. We've lost count of how many phases we have run (and we would probably disagree on how to count it), but the Galaxy Zoo Wikipedia page says it's been at least 15.